Strength and Conditioning for Team Sports
Strength and Conditioning for Team Sports is designed to help devise more
effective high-performance training programmes for team sports. This
textbook remains the only evidence-based study of sport-specific practice to
focus on team sports and features all-new chapters, including one on
neuromuscular training, and dedicated chapters exploring injury prevention
and the specific injury risks for different team sports. Fully revised and
updated throughout, the new edition also includes the addition of over 200
new references to the research literature in the field.
This book addresses the core science underpinning different facets of
physical preparation, covering all aspects of training prescription and the key
components of any degree course related to strength and conditioning,
including:
• physiological and performance testing;
• strength training;
• metabolic conditioning;
• power training;
• agility and speed development;
• training for core stability;
• training periodisation;
• training for injury prevention.
Bridging the traditional gap between sports science research and practice in
the field, each chapter features guidelines for evidence-based best practice, as
well as recommendations for approaches to physical preparation to meet the
specific needs of team sports players. This new edition also includes an
appendix that provides detailed examples of training programmes for a range
of team sports. Fully illustrated throughout, it is essential reading for all
serious students of strength and conditioning, and for any practitioner seeking
to extend their professional practice.
Paul Gamble has worked in high-performance sport for over a decade, during
which time he has coached elite athletes in an array of sports and at all ages
and stages of development. Paul began his career working in professional
rugby with English Premiership side London Irish, and has since worked in a
range of sports, most recently serving as National Strength and Conditioning
Lead for Scottish Squash. He has published a number of articles in peerreviewed journals, chapters in edited textbooks and has previously written
two textbooks as sole author.
STRENGTH AND CONDITIONING
FOR TEAM SPORTS
Sport-specific physical preparation for high
performance, second edition
Paul Gamble
First published 2009 by Routledge
This edition published 2013
2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN
Simultaneously published in the USA and Canada
by Routledge
711 Third Avenue, New York, NY 10017
Routledge is an imprint of the Taylor & Francis Group, an informa business
© 2013 Paul Gamble
The right of Paul Gamble to be identified as author of this work has been asserted by him in
accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this book may be reprinted or reproduced or utilised in any
form or by any electronic, mechanical, or other means, now known or hereafter invented,
including photocopying and recording, or in any information storage or retrieval system,
without permission in writing from the publishers.
Trademark notice: Product or corporate names may be trademarks or registered trademarks,
and are used only for identification and explanation without intent to infringe.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
Gamble, Paul.
Strength and conditioning for team sports : sport-specific physical preparation for high
performance / by Paul Gamble. -- 2nd ed.
p. cm.
1. Sports--Physiological aspects. 2. Sports teams--Physiological aspects.
3. Physical education and training. 4. Athletes--Training of. I. Title.
GV711.5.G345 2012
613.7’11--dc23
2012016560
ISBN: 978-0-415-63792-3 (hbk)
ISBN: 978-0-415-63793-0 (pbk)
ISBN: 978-0-203-08425-0 (ebk)
Typeset in Bembo and ITC Stone Sans
by Bookcraft Ltd, Stroud, Gloucestershire
CONTENTS
List of tables
List of figures
Acknowledgements
1 Principles of specificity and transfer of training effects
2 Assessing physiological and performance parameters
3 Neuromuscular training
4 Metabolic conditioning
5 Strength training
6 Training for power
7 Sports speed and agility development
8 Lumbopelvic ‘core’ stability
9 Training for injury prevention: identifying risk factors
10 Training for injury prevention: specific training interventions
11 Planning and scheduling: periodisation of training
12 Physical preparation for youth sports
Appendix – Practical examples of training design
References
Index
TABLES
2.1 Selected repeated sprint ability test protocols
11.1 Representative off-season training mesocycle
11.2 Representative pre-season training mesocycle
11.3 Representative in-season training mesocycle
11.4 Representative ‘peaking’ training mesocycle
12.1 Training guidelines: prepubescent players
12.2 Training guidelines: early puberty
12.3 Training guidelines: adolescent players
FIGURES
3.1 The role of neuromuscular function schematic
3.2 Single-leg balance and head turn on domed device
3.3 Compass bound and stabilise onto domed device
5.1 Barbell single-leg squat
5.2 Barbell step up
5.3 Front racked barbell diagonal lunge
5.4 Barbell lateral step up
5.5 Alternate arm incline dumbbell bench press
5.6 Barbell overhead step up
5.7 Dumbbell clockwork lunge
5.8 Alternate arm cable fly
5.9 Single-arm cable row
6.1 Barbell split jerk
6.2 Barbell split clean
6.3 Barbell bound step up
6.4 Alternate leg split bounds
7.1 Cable resisted cross-over lateral lunge
7.2 Alternate leg lateral box skips
8.1 Alternate arm cable lat pulldown
8.2 Side bridge on domed device
8.3 Swiss ball bridge with leg raise
8.4 Single-leg alternate arm cable press
8.5 Swiss ball Russian twist
10.1 Low box single-leg knee and ankle flexion
10.2 Single-leg hip flexion and extension on domed device
10.3 Single-leg dumbbell straight-legged deadlift
10.4 Side bridge ‘wipers’ on domed device
10.5 Prone dumbbell external rotation
10.6 Prone dumbbell lateral raise
10.7 Alternate arm cable reverse fly
10.8 Cable diagonal pulley
11.1 Periodisation of exercise selection schematic
12.1 Swiss ball suspended row
12.2 In-line single-leg squat
12.3 Dumbbell split squat
ACKNOWLEDGEMENTS
I am keenly aware what a privileged position it is to be able to work in
performance sport, and I must thank all those coaches and athletes I have been
fortunate enough to work with and learn from. Equally, I strongly believe the
responsibility of training athletes is a right that must be earned and I hope the
information presented in this book assists aspiring strength and conditioning
specialists in that quest.
Once more this book is for Sian.
1
PRINCIPLES OF SPECIFICITY AND TRANSFER OF
TRAINING EFFECTS
Introduction
Specificity of training is increasingly acknowledged as fundamental in
shaping training responses (Kraemer et al. 2002). Training specificity
encapsulates two key concepts. The first is that the nature of acute training
responses will be dependent upon – hence specific to – the nature of the
particular training stimulus. The second, a corollary of the first, is that the
degree to which training resembles – is specific to – conditions faced during
competition influences the degree to which training effects will transfer to
performance in the short term. These two concepts therefore relate to all
aspects of physical preparation.
The essence of training specificity is that training responses elicited by a
given exercise mode are directly related to the physiological elements
involved in coping with the specific exercise stress (Kraemer et al. 2002).
Accordingly, the strength and conditioning specialist can expect very little
impact upon muscles and metabolic pathways that are not directly engaged
during the particular exercise (Millet et al. 2002b).
The degree of carry-over from training to competition is described in terms
of transfer of training effect (Stone et al. 2000). In the short term, this is
heavily influenced by the level of mechanical and bioenergetic (energy
systems) specificity of training in relation to competition. The probability that
a training intervention will be reflected in performance changes therefore
depends upon the degree to which training replicates the constraints of that
aspect of athletic performance (Gamble 2006).
The impact that training specificity has on training outcomes also grows
with exposure to training (Young 2006). With advances in training experience,
training specificity influences the athlete’s training responses to an increasing
degree. Hence, factors relating to specificity assume increased relevance and
importance at later stages of development. Training specificity therefore
becomes a critical consideration as athletes approach elite levels of
performance.
Presented is an outline of general principles of specificity, and a discussion
of how they relate to training. Brief examples of the ways in which specificity
is manifested are also given. Finally, the implications of this information for
coaches and athletes and how this should be implemented when designing
training plans will be discussed.
Principle of individuality
Inherited traits will influence athletes’ performance capacities and trainability
for a particular physiological property (Beunen and Thomis 2006). The
‘internal training load’ exerted upon the athlete and the timeframe and
magnitude of training responses are therefore to some extent specific to the
individual.
Genotype influences the individual athlete’s responsiveness to a particular
form of training, and also effectively sets the ceiling for any training effect
(Smith 2003). These factors will impact upon both the rate of development and
also the upper ceiling for training adaptation for each individual. The athlete’s
genotype exerts considerable influence upon athletic capabilities such as
speed, power, strength and cardiorespiratory endurance, and their propensity
for developing these qualities (Beunen and Thomis 2006). For example,
hereditary factors are reported to account for 47 per cent of the variability in
an individual’s trainability with respect to the relative VO2max response to
training (Bouchard 2011).
Although genetic potential may be beyond the control of the coach and
athlete, the training performed and the environment the athlete is exposed to
will influence the degree to which inherited traits are expressed (Beunen and
Thomis 2006). This is the phenotype of the athlete, which will be specific to
the history of the individual and other environmental factors (Smith 2003).
Phenotypic expression of physical qualities is thus determined by the
interaction of genetics, the athlete’s training and other environmental factors
(Beunen and Thomis 2006). In a squad setting, even with a fixed external
training load, such factors will determine the specific ‘internal load’ placed
upon each athlete, which in turn will define their individual training response
to the training prescribed (Impellizzeri et al. 2005).
The degree to which athletes’ inherited traits translate into performance
abilities in the competition arena will depend not only upon the quality of the
training prescribed, but also athletes’ motivation and dedication when
undertaking training. Likewise, the key technical and tactics elements that
determine success in skill sports are teachable (Smith 2003). The quality of
coaching and the coach–athlete interaction are thus important factors. The
athlete’s personality traits will further determine the effectiveness of physical
preparation as well as both athletic and sports skill acquisition. Self-discipline,
appetite for work and willingness to learn are all important in determining
whether the athlete fulfils the many hours of quality training and practice
required for elite-level performance (Smith 2003).
Process of training adaptation
Broadly, the process of training adaptation is that exposure to an effective
training stimulus prompts the physiological and/or neuromuscular systems
affected to respond by increasing their capacities in order to be better able to
cope if faced with a similar challenge in the future. The original theoretical
basis of training adaptation is the general adaptation syndrome (GAS)
proposed by Hans Seyle (Seyle 1956), which describes a generic response of an
organism to a stressor (Wathen et al. 2000). According to this model, the first
phase of response to any stressor is characterised as shock or alarm (Brown
and Greenwood 2005). Following this is a supercompensation phase, whereby
the body adapts to increase the specific capabilities affected by the particular
stressor. Over time if the stressor continues the organism may enter a terminal
phase, termed maladaptation (Brown and Greenwood 2005).
However, each individual physical capacity has its own individual window
of adaptation:
• the rate of adaptation varies according to the individual athlete (genetic
factors) and also depends upon their training history – that is, how much
adaptation has already taken place;
• the total degree of adaptation that is possible is dependent on genetic
aspects, which effectively set the ceiling for adaptation of a particular
physical capacity for each athlete.
Accordingly, this GAS paradigm has since been refined by the fitness–fatigue
model (Chiu and Barnes 2003; Plisk and Stone 2003). A key distinction is that
the fitness–fatigue model differentiates between the actions of a given stressor
on individual neuromuscular and metabolic systems (Chiu and Barnes 2003).
A corollary of this is that there are effectively individual windows for
adaptation for each physical capacity. Particular acute adaptive responses are
described as being restricted and specific to the systems employed in the
training stimulus. The fitness–fatigue model also stipulates that the extent and
length of any short-term effects following training are specific to the training
stimulus – rather than a generic response (Chiu and Barnes 2003).
The other major advancement of the fitness–fatigue model is that it
describes a dual adaptive response – resulting in both fitness and fatigue aftereffects, as opposed to the single common response described by GAS. These
fitness and fatigue responses exert opposing effects on performance and are
described as having defined characteristics: there are distinct differences in
both magnitude and duration of fitness versus fatigue responses (Chiu and
Barnes 2003). The athlete’s physiological status is effectively determined by
the net effect of these two opposing factors at that given time (Chiu and
Barnes 2003).
Specificity in relation to training experience and
athletic status
The extent to which specificity principles apply appears to vary according to
initial training status and degree of training experience (Young 2006). In
untrained individuals, training specificity does not exert the same level of
influence as that observed with trained individuals. This is illustrated by the
responses of untrained subjects to endurance training. Following training,
untrained and recreationally trained individuals often demonstrate improved
endurance scores on other exercise modes (Millet et al. 2002). This is not the
case with elite athletes; what limited cross training effects have been observed
in trained athletes fall far short of performance improvements elicited by
mode-specific training (Millet et al. 2002).
The limiting factor in terms of oxygen transport also appears to vary
between untrained individuals and athletes (Hoff 2005). The muscles of
untrained subjects are not fully able to utilise available oxygen delivered via
the blood. Conversely, the locomotor muscles of trained individuals have the
capacity to handle significantly more oxygenated blood than the heart is able
to pump. Hence, for athletes during dynamic activity utilising large muscles –
as occurs in team sports – the limiting factor is their cardiac output (Hoff
2005).
There is also evidence that the relationship between stroke volumes and
VO2 is also different for well-trained versus moderately and untrained
individuals (Hoff 2005). What occurs in the untrained and moderately trained
is the classical textbook pattern of a levelling off in stroke volume as
workloads increase beyond around 60 per cent VO2max (Hoff 2005). However,
it is apparent that well-trained athletes continue to increase stroke volume
with increasing workloads up to VO2max (Hoff 2005).
A similar scenario is evident with strength training. Almost any training
represents a novel stimulus to the untrained neuromuscular system. As a
result, untrained individuals demonstrate an array of training effects,
regardless of the nature of the training (Newton and Kraemer 1994).
Consequently, a wide variety of training interventions will produce
favourable adaptations in a given aspect of neuromuscular performance with
untrained individuals (Kraemer et al. 2002). Again, this is not the case in
advanced lifters and elite strength-trained athletes.
There is increasing evidence that the dose – response relationships
pertaining to volume, frequency and intensity of strength training are specific
to the level of training experience and athletic status of the individual
(Peterson et al. 2004; Rhea et al. 2003). The optimal strength training
prescriptions differ for untrained individuals and those with strength training
experience. Examination of training studies reveals that subject groups
comprising strength-trained athletes differ markedly on all three of these
training variables in comparison to both untrained and trained non-athletes
(Peterson et al. 2004; Rhea et al. 2003). The trends in each training parameter
between groups appear to form a continuum of optimal levels of volume,
frequency and intensity with progression in training experience and athletic
status.
Specificity of training
A foundation of training is described by the acronym SAID: specific
adaptation to imposed demands (Baechle et al. 2000). Simply, any
physiological adaptation produced is dependent on the specific form of
overload provided by the training stimulus (Stone et al. 2000).
Metabolic specificity
Metabolic specificity of training adaptations applies to the energy systems
mobilised during exercise. The amount of muscle mass involved and overall
exercise intensity dictate the scope of central and peripheral training effects.
For example, these factors will determine whether training responses are
limited to adaptations at muscle level, or if central cardiovascular changes are
elicited (Millet et al. 2002).
Training mode specificity can also be observed with metabolic
conditioning. The running and cycling training completed by elite triathletes
are shown to be unrelated to their swim performance (Millet et al. 2002).
Accordingly, improved performance measured via a swimming test mode
following swim training is not reflected in treadmill test scores. In trained
non-athletes, cross training (swimming) is likewise shown to be inferior to
running training in improving running performance parameters (Foster et al.
1997).
Adaptations following purely anaerobic training are mainly restricted to
increased activity of enzymes involved in anaerobic metabolism (Wilmore and
Costill 1999). Conversely, continuous submaximal aerobic training is reflected
in improved oxidative enzymes, whilst the anaerobic enzyme profile remains
largely unchanged (Wilmore and Costill 1999). Eliciting anaerobic adaptations
requires anaerobic training, whereas improvements in oxidative capacity can
only be derived using conditioning activities that stress the aerobic system.
It has been suggested that high-intensity sprint interval training methods
defy the principles of specificity on the basis that this approach is observed to
produce gains in oxidative capacity despite the fact that this form of training
consists of maximal 30-second sprints, with extensive rest between, and
greatly reduced overall training volume (Burgomaster et al. 2008). However,
this form of training does in fact engage and stress oxidative metabolic
systems, and the contribution from aerobic metabolism increases markedly
during successive work bouts (Bogdanis et al. 1996a; Ross and Leveritt 2001).
Equally, the training adaptations remain specific to the form of training. The
nature of the training response differs between high-intensity interval
training, which elicits predominantly peripheral adaptations, and
conventional endurance training, which is associated with both central and
peripheral adaptations (Bishop et al. 2004).
Depending on the format, interval training with shorter (that is,
incomplete) rest intervals may maximally stress both aerobic and anaerobic
systems (Tabata et al. 1996, 1997). This training format can thus exhibit a
combined training response. The specific training adaptation elicited,
however, remains dependent upon the format of interval training, and factors
such as the intensity of work intervals and the particular work:rest ratios
employed (Spencer et al. 2005).
Biomechanical specificity
Biomechanical specificity concerns parameters of training that include range
of motion and joint angles (Stone et al. 2000a). This is applicable both to
dynamic and isometric training, with superior strength gains observed within
the range of motion and at the joint angles featured in training (Morrissey et
al. 1995). Based upon these observations, it follows that exercise selection
should reflect the full range of motion and joint angles featured in the sport or
athletic activity. This is particularly important for certain muscle groups such
as the hip extensors, especially the hamstrings. For these muscles the profile of
peak torque versus joint angle is identified as being critical for healthy
function and protecting against injury (Heiderscheidt et al. 2010). Accordingly
it is very important that the training for these muscles replicates the joint
ranges of motion required during athletic activities, for example running and
sprinting.
Biomechanical specificity also extends to aspects such as posture and limb
position. Consequently, greatest strength responses are manifested during
closed kinetic chain movements following closed kinetic chain training,
whereas the opposite applies to open kinetic chain exercises (Stone et al. 2000).
Similarly, a lift performed in a standing position (for example, barbell squat)
has greater carry-over to most types of athletic performance than a similar
movement performed in a seated or supine position (for example, leg press).
Biomechanical specificity is also evident in the relationship between
unilateral (singlelimb) and bilateral (both limbs working simultaneously)
strength measures (Enoka 1997; Newton and Kraemer 1994). Cyclists are
shown to exhibit greater overall strength when single-leg press scores are
summed in comparison to their bilateral leg press score – an effect known as
‘bilateral deficit’ (Enoka 1997). This reflects the fact that cyclists work
unilaterally – alternately exerting force with each leg – during training and
competition. Conversely, athletes for whom training is bilateral can exhibit
bilateral facilitation (Enoka 1997). For example, it is reported that rowers’
bilateral leg press scores are greater than the sum of their single-leg press
scores (Enoka 1997; Newton and Kraemer 1994). It follows that exercise
selection should emphasise either bilateral or unilateral movements,
corresponding to what occurs during competition in the sport or athletic
event.
Finally, training effects are specific to the muscle contraction type
employed in the training exercise (that is, concentric, eccentric or isometric)
(Morrissey et al. 1995). Consequently, superior strength scores post-training
are observed in measures that feature the same mode of contraction as that
employed in training (Morrissey et al. 1995). For example, isometric training
elicits greater isometric strength improvement (registered under static
conditions) than dynamic strength training (Morrissey et al. 1995).
Contraction-type specificity is also observed in the finding that eccentric
training interventions are associated with training responses, such as changes
in torque – joint angle relationships (Brockett et al. 2001), which are not seen
with concentric training modes (Rees et al. 2009).
Kinetic and kinematic specificity
In addition to biomechanical factors, other aspects of movement including
relative force, velocity and timing characteristics are also important. Such
considerations
include
magnitude
and
duration
of
loading,
acceleration/deceleration profile of the movement, and movement velocity.
The duration and rate of force generation for a particular athletic task have
a major bearing on the degree of statistical relationship observed with other
measures, despite similarities in biomechanics between tasks (Cronin and
Sleivert 2005). For example, jump squat training was reported to produce gains
in jump height that were not seen in the subject group trained with traditional
barbell squat and leg press, despite the two training modes having very
similar biomechanical characteristics (Newton et al. 1999). Differences in
acceleration and rate of force development between the two training modes
were suggested to account for the difference in training effects observed.
Contraction-type specificity is also observed and this serves to determine
the nature of training responses elicited by particular strength and speedstrength training modes. For example, changes in the eccentric phase of
activities such as jumping that are preceded with a countermovement and
improvements in coupling of eccentric–concentric components are only
observed with training modes that feature these elements (Cormie et al.
2010a).
Velocity specificity is evident in that strength gains will tend to be
restricted to the velocities at which the muscles are trained (Morrissey et al.
1995). It appears that there is a greater degree of velocity specificity in training
responses at the higher end of the training velocity spectrum (Morrissey et al.
1995). At slower contraction speeds there may be some carry-over to velocities
at and below the training velocity. In contrast, within the upper region of the
force–velocity curve, strength improvements are typically only registered
within the narrow range of velocities used in training (Morrissey et al. 1995).
Psychological specificity
Physiological capabilities are manifested in a sports setting as part of coordinated and skilled movements. A corollary of this is that strength and
conditioning specialists should consider the context in which physiological
training is performed (Siff 2002). Specificity considerations therefore also
include psychological aspects of performance conditions. Cognitive and
perceptual elements of performance conditions should likewise be accounted
for in training design (Ives and Shelley 2003).
The principles of specificity thus also apply to psychological aspects. For
athletes in team sports in particular, physical and mental capabilities are
irrevocably linked. Three crucial interrelated components that are identified as
influencing training responses are attention, mental effort and intention (Ives
and Shelley 2003):
Attention is a key factor in perception–action coupling and the superior
decision-making of elite performers. Elite athletes attend to relevant cues from
the competition environment and process them better as the basis for their
movement responses (Ives and Shelley 2003). During competition and
practices, attention is also crucial to anticipatory responses and associated
postural and motor control. The athlete’s locus of attention, in terms of
whether it is externally or internally focused, is shown to impact upon motor
learning and performance (Ives and Shelley 2003).
It is recognised that directed mental effort has the potential to directly
affect the magnitude of training responses (Ives and Shelley 2003). Conscious
effort to exert maximal force has been found to significantly influence gains
in strength and power (Jones et al. 1999). It has been reported that greater
gains in strength are manifested when subjects were specifically instructed to
focus on maximally accelerating the barbell for every repetition, as opposed to
lifting without specific focus or instruction (Jones et al. 1999).
Intent is integral to neural factors associated with adaptations in highvelocity strength and rate of force development (Behm and Sale 1993; Ives and
Shelley 2003). Recruitment and firing of muscles during training are in part
dictated by what is anticipated prior to the movement (Behm and Sale 1993;
Behm 1995). An illustration of this is that training effects associated with
ballistic training can be derived with isometric training under certain
conditions. If the lifter trains with the conscious intention of moving the static
resistance explosively, significant improvements in rate of force development
can take place – despite the fact that no movement actually takes place (Behm
and Sale 1993). Physiological adaptations are thus specific to and partially
determined by the intention and corresponding neuromuscular patterns
during training (Ives and Shelley 2003).
It is important therefore to consider not only mechanical and metabolic
specificity, but also to address other aspects of the training environment.
Imposing sport-specific constraints may help appropriately shape training
movement responses. It is suggested this approach may encourage more
adaptive learning and likewise develop decision-making (Ives and Shelley
2003).
Conversely, excessively restricting training either by mechanically fixing
the planes and range of movement or through overtly prescriptive coaching
intervention will tend to discourage development of directed mental effort,
task-specific attention, and sport-specific intent (Handford et al. 1997).
Conducting physiological training in isolation from the athletic performance
the athlete is training for is likely to hinder transfer of training effects (Ives
and Shelley 2003).
The paradox of specificity and transfer of training
effects
Theoretically, the most ‘sport-specific’ or ‘functional’ form of training is to
perform the actual movement(s) of the sport (Siff 2002), although this
assertion does neglect the element of overload required to elicit a training
response. That said, the major implication of training specificity is that
training modes which correspond most closely to the target activity can be
expected to result in the greatest direct transfer of training effects in the short
term. However, the paradox of training design is that over the long term the
most task-specific training employed in isolation is unlikely to provide the
development of the foundation qualities required to ultimately achieve
optimal performance (Bondarchuk 2007).
An example from strength training is that ‘non-specific’ heavy resistance
training modes are required initially in order to best develop underlying
contractile properties and morphological aspects for high-intensity
performance (such as sprinting). This is also the case for metabolic
conditioning: whilst performing repetitions over 200m with complete rest
between might seem the most ‘specific’ approach for a 200m runner, during
the earlier stages of the training year these athletes will in fact benefit more
from performing a range of sessions over various distances, with varying
(incomplete) rest intervals. Although these sessions appear on the surface to
be less specific to the constraints of a performing a 200m race in competition,
this approach will over time provide the foundation development of oxidative
capacities and anaerobic capacity that will allow the athlete to train and
compete at high intensity later in the competition season.
It is therefore critical that the strength and conditioning specialist is
mindful of both short-term and long-term training adaptation and the
underlying processes involved (Bondarchuk 2007). As has been described in
the previous sections, specificity is a key factor that governs training
responses in the short term; however, a longer-term perspective is also
required in order to best organise training to ultimately take full advantage of
transfer of training at the critical periods of the competition phase in the
calendar.
As will be discussed in a later chapter, is equally important that there is
variation in exercise selection throughout the training year in order to avoid
plateaus in training adaption. It would appear, therefore, that what will be
required is a coherent progression during the course of the training
macrocycle through a range of exercises that span the specificity spectrum
(Gamble 2011d).
Accounting for specificity in training programme design
The first step in deriving the benefits of training specificity is a thorough
needs analysis. One aspect of this is identifying the biomechanics and
bioenergetics associated with the particular sport or playing position. By
defining the specific demands of competition it will be possible to account for
the relevant parameters in the design of players’ training. Another aspect of
the needs analysis process involves identifying the individual profile of each
athlete in terms of different aspects of physical preparedness.
Considerations for biomechanical specificity include direction and range of
movement, type of muscle contraction, movement velocity and the rate and
duration of force development (Stone et al. 2000). Exercise selection should
cater for the full range of motion identified from competition, as well as the
conditions under which movements are initiated (Sheppard 2003). The degree
of loading that is appropriate will vary according to the movement. In the case
of fine motor skills, excessive loading may interfere with the proper execution
of the movement (van den Tillar 2004).
Applying metabolic specificity basically requires that the format of
conditioning reflects the parameters of competition. One approach used in
other sports and athletic events involves setting target training paces, based
upon actual or desired competition performance (Plisk and Gambetta 1997).
Identifying such parameters (work rates, movement patterns, work:rest ratios)
in order to design sport-specific conditioning programmes for team sports
poses a greater challenge. This will be explored further in a later chapter.
Performance benefits may be derived by accounting for psychological
aspects in the training environment. There are early indications that
incorporating practice-related cognitive strategies during training leads to
greater carry-over of training effects to sports performance (Ives and Shelley
2003). For example, visual and verbal cueing has been suggested to enhance
the effectiveness of plyometric jump training for volleyball players (Ives and
Shelley 2003). In the case of strength training, psychological interventions may
take the form of mental imagery or specific cueing to lift explosively from the
strength coach whilst lifting (Jones et al. 1999).
Coaches must also recognise that skill level and training experience
influence the training parameters that will be effective in developing athletic
performance (Cronin et al. 2001b; Peterson et al. 2004; Rhea et al. 2003). With
progression in training status, training specificity assumes further importance.
It would appear to follow that programme design must ultimately become
increasingly specific to elicit the desired response when addressing a
particular aspect of performance (Newton and Kraemer 1994).
Finally, training should be tailored to the specific needs and constraints of
the individual. The delivery of training should be responsive to the relative
stresses placed upon each individual, and coaches should recognise that the
time course and magnitude of gains will also vary between athletes. Each
athlete will also have different relative strengths and weaknesses, both of
which should be accounted for in their individual training programme.
Players will also vary in terms of their tolerance and responsiveness to
different forms of training.
2
ASSESSING PHYSIOLOGICAL AND PERFORMANCE
PARAMETERS
Introduction
The principles of training specificity have implications when assessing athletic
performance (Abernethy et al. 1995). Fundamentally, in order to be relevant,
any physiological tests selected must match the specific capabilities identified
as contributing to performance in the sport (Bosquet et al. 2002). For team
sports this requires consideration of not only the sport but also the playing
position.
It follows that physiological tests selected should therefore be specific to the
sport the player is training for (Murphy and Wilson 1997). Tests that are most
game-specific tend to be given greatest credence by those involved in the
sport. In basketball, the vertical jump test is shown to be the best predictor of
playing time given to players of any athletic performance test (Hoffman et al.
1996). This is a reflection of the specificity – and hence relevance to
performance – of vertical jump testing for basketball players.
Test specificity is again manifested in the observation that the greatest
degree of improvement in muscle function following training is registered
with the test modality that most closely matches the training movement
(Morrissey et al. 1995). It follows that testing should be specific to the
movement patterns and velocity used in training in order to be sensitive to
training-induced changes in muscle function (Abernethy et al. 1995).
Fundamentally, training is aimed at improving the player’s performance.
From this point of view, physiological tests should ultimately be judged upon
the extent that they reflect changes in sports performance (Murphy and
Wilson 1997). In order to be relevant, tests must not only be sensitive to
adaptations elicited by the training intervention but also capable of registering
any resulting improvements in performance (Murphy and Wilson 1997).
One consideration with test specificity is taking account of the conditions
under which tests of muscle function are measured. For example,
neuromuscular properties such as rate of force development (RFD) and highvelocity strength are relevant to dynamic performance (Newton and Kraemer
1994). However, the corresponding test measures for these capabilities are
only related to athletic performance if they are measured under appropriate
conditions (Wilson et al. 1995).
Rationale for testing team sports players
Testing in sport is typically undertaken with one of three broad aims in mind:
1 The first of these is to evaluate the abilities or current state of preparedness
of the player in the context of the demands of their sport (Impellizzeri et al.
2005); this may be:
• from a talent identification viewpoint (Abernethy et al. 1995), or
• in order to identify specific strengths and weaknesses of the players
assessed in order to prioritise different training goals for the individual
(Lemmink et al. 2004).
2 The second application of testing is to monitor progression and evaluate the
effectiveness of training prescribed (Abernethy et al. 1995, Impellizzeri et al.
2005).
3 Finally, testing can be undertaken for training prescription purposes – for
example, setting individualised training intensity parameters based on the
evaluated capacities of each player (Buchheit 2008).
Application of testing in team sports
There are notable cases in sport where players’ scores on a particular battery
of performance tests are given a great deal of credence by those involved in
the sport. Possibly the best example of this is the National Football League
Combine – the standard battery of tests that is employed for selection in
professional American football. Performance on these tests has been identified
as a significant factor that distinguishes players successful in being drafted
onto NFL teams from those who were unsuccessful (Sierer et al. 2008). In
recognition of this, some authors have advocated targeted training to improve
a player’s performance specifically for particular tests that hold a lot of weight
in the sport, with the aim of improving their prospects of selection – and the
prospective financial rewards of signing professional contracts (McGee and
Burkett 2003). Indeed, the degree to which players’ performance on these tests
apparently influences players’ chances of selection has led entrepreneurial
strength coaches to adopt the approach of training players specifically for the
NFL Combine assessments, as opposed to preparing them to compete in the
sport. Increasingly this is becoming standard practice in the strength and
conditioning ‘industry’.
The application of testing to guide training goals in the context of strength
and power training has been described as ‘strength diagnosis’ (Wilson and
Murphy 1996). In this way a player’s relative scores on different measures of
muscular performance, in relation to the demands associated with the sport,
provide a means to identify deficits in particular areas. Addressing the areas
of relative weakness identified then becomes the priority in the player’s
subsequent training block.
As mentioned in the previous section, testing is also employed directly to
prescribe training intensity. Examples include strength training where
intensity for a given exercise may be prescribed as percentages of a player’s
one-repetition maximum for that lift. Similarly, intensity for endurance
training can be prescribed as percentage of the player’s recorded maximum
oxygen uptake (VO2max), heart rate maximum (HRmax), or more commonly,
their maximum aerobic speed derived from testing (Buchheit 2008).
Testing is also widely used to track improvements in players’ fitness and
performance, and as a means to assess the effectiveness of training prescribed
(Impellizzeri et al. 2005). One consideration with team sports is that the
individual stimulus provided by training prescribed to a group of players will
vary for each player. Even if the external load in terms of intensity and
volume prescribed is constant, genetic endowment and training background
will both influence the magnitude of the ‘internal load’ imposed upon each
player, which will in turn affect their individual training response
(Impellizzeri et al. 2005). In view of this, testing will only provide a partial
reflection of the effectiveness of the training prescribed, unless accompanied
by ongoing monitoring and manipulation of players’ individual daily training
load. By extension, it follows that evaluating the day-to-day training process
is as important as periodic assessment of the training outcome in order to
determine the effectiveness of the training programme (Impellizzeri et al.
2005).
Utility and practical relevance of physiological and
performance tests
Whether testing is carried out in the laboratory or in the field, both reliability
and validity are key issues (Reilly et al. 2009). Reliability pertains to how
consistent the scores of the given test are – hence how repeatable the test is.
Validity concerns the extent to which the test actually measures the physical
capability it is intended to assess. Both criteria must be met for any given test
to be of any value as a means for assessing players’ performance. It is possible
to have a reliable test – one that gives highly consistent scores – that may not
necessarily be a valid test, in terms of its ability to measure the particular
aspect of motor performance the coach wishes to assess. Conversely, a highly
valid test from the point of view of closely reflecting the movement or aspect
of performance the test is designed to measure is of little value if it is not
reliable in terms of producing consistent scores. In the latter case, the tester
cannot be confident that any measured change over time is due to actual
change in performance rather than just the error inherent in the test measure.
A good illustration of this comes from basketball, where a sport-specific test
battery was designed to measure performance capabilities, which the authors
named the Performance Index Evaluation (PIE) (Barfield et al. 2007). The tests
chosen appeared highly specific to the sport of basketball; however, further
investigation of the validity and reliability of the PIE with male and female
collegiate players revealed it to have unacceptable test–retest reliability.
Furthermore, the PIE showed scores that also appeared to lack criterionrelated validity on the basis that they failed to correlate to playing time
allocated to these collegiate players (Barfield et al. 2007).
In order to provide a framework within which players can then be
evaluated, it is important to identify the specific parameters that influence
performance for the particular sport (Muller et al. 2000). Once identified, tests
that are sensitive enough to discern changes in the particular parameter
should be sought. Specificity considerations have a major bearing on both
these aspects. In order to be relevant, the parameter must be specific to
performance of the sport in question, and correspondingly the test measure
must be specific and therefore sensitive to the parameter the coach wishes to
test.
One approach is to identify potentially important aspects of motor
performance based upon qualitative assessment of the sport and then identify
tests that are designed to measure each of these areas (Muller et al. 2000). The
next step is for players competing at different levels to undergo the battery of
motor performance tests derived. The degree to which each test correlates to
players’ level of performance can be taken as an indication of the importance
of the corresponding parameter to success in the sport (Muller et al. 2000). In
this way the tests that appear most strongly associated with success in the
sport can be identified. However, one major caveat to this approach is that it
is not safe to assume a causal relationship based solely on an apparent
statistical relationship from a single set of measurements. Whilst two
measures may show an apparent correlation from a one-off measurement, it
has been demonstrated that with repeated measurement the relationship
between performance measures may diverge over time (Nimphius et al. 2010).
A better, albeit more time-consuming, approach may therefore be to assess the
relationship between measures over time, via periodic repeated assessment.
Biomechanical specificity is a key factor with respect to test specificity, but
it is only part of the equation. Other elements such as acceleration–
deceleration profiles may be equally important. An illustration of this is the
difference between barbell squat repetition maximum and barbell jump squat
assessments, and their relationship with dynamic measures of performance
such as sprint times with team sports players. In the case of the barbell squat
3-repetition maximum (3-RM) test, no relation to sprint performance was
found over any distance, whereas barbell jump squat test scores were
observed to be significantly correlated to 5m, 10m, and 30m speed of
professional and semi-professional rugby league players (Cronin and Hansen
2005). Players’ 3-RM squat and jump squat scores were also not related to
each other in this study, despite the fact that the two movements are
biomechanically very similar.
If the objective of testing is to evaluate the effectiveness of players’ training,
then specificity with regard to the training used must be considered. Greatest
effects are observed during testing at velocities in the range featured in
training (Morrissey et al. 1995). It follows that testing should be specific to the
movement patterns and velocity used in training in order to be sensitive to
training-induced changes in muscle function (Abernethy et al. 1995).
However, it is not sufficient for test measures to be specific only to the type of
training employed. Testing to monitor training effects must also bear relation
to the sport in order to be sensitive to sports performance. When these
conditions are not met, improvements in neuromuscular and athletic
performance (maximum strength and sprint scores) can be observed following
training despite the chosen test measures registering no change (Murphy and
Wilson 1997). The particular test mode and outcome measures chosen must
therefore be selected carefully in order to meet the objective of monitoring the
effectiveness of players’ physical preparation (Cronin and Hansen 2005).
Practicality of test modes for athletic assessment
Two major issues concerning modes for physiological and performance
assessment are cost (expense of test apparatus and skilled personnel to operate
it) and time demand. Considering both these factors – aside from concerns
regarding specificity and relevance – individual laboratory assessment for
large squads of players is not likely to be affordable or practical. Field-based
tests are generally more conducive to team sports testing as these can be
conducted in the field (avoiding the related travel and cost implications of
using a laboratory) and also enable larger numbers to be tested in a relatively
shorter time than tends to be possible with laboratory-based testing.
Whatever the mode of assessment, subject motivation is a crucial factor.
Field tests have more obvious relevance from the players’ viewpoint, and also
benefit from context specificity: field tests are conducted in a setting where
the players habitually train and perform as opposed to the more alien
environment of a laboratory. In addition, field tests can be carried out with
larger numbers of players, which allows those conducting the test to
incorporate a competitive element. Because of these factors, field-based tests
are therefore likely to engender greater compliance and motivation among
team sports players, which improve the chance of consistent and maximal
effort when testing is repeated over a period.
Design of field-test protocols are often modified in an attempt to make
them more specific to the sport. Many sport-specific field tests are described in
the literature (Barfield et al. 2007; Graham et al. 2003; Mirkov et al. 2008).
With any ‘sport-specific’ field test there is inevitably a trade-off between
replicating game conditions and standardising test conditions to obtain a
reliable measure. Likewise, with any novel test protocol there is a need for
sufficient normative data for the sporting population in question to provide a
reference for comparison.
Scheduling of testing
Testing is only useful to the extent that it is repeated at regular intervals. Only
in this way can progress be monitored or issues affecting performance be
identified (for example, errors in training design, competition and other
stressors). From this viewpoint it is very important that the test battery is
carefully selected in order to be time-efficient, and can therefore be
undertaken on a regular basis without excessive disruption to the training
schedule. That said, the full battery of tests need not be undertaken at every
test session: an abridged version of the test battery can be used during most
regular test sessions and the full array of tests reserved for key points in the
training year.
Strength assessment
Maximum strength
Strength is generally defined as maximal force or torque generated during a
maximal voluntary contraction under a given set of conditions. Key
parameters include posture, nature of the movement employed (single-joint
versus complex multi-joint movements), contraction type and movement
velocity (Abernethy et al. 1995). Broadly, strength qualities can be categorised
in terms of static, concentric and eccentric modes of contraction. In
recognition of the force–velocity curve, authors similarly make a distinction
between low-velocity maximum strength and strength expressed at high
movement velocities.
Modes of strength assessment can be categorised as ‘isometric’, ‘isokinetic’
or ‘isoinertial’.
Isometric strength assessment
Isometric assessment typically uses a force transducer integrated into fixed
apparatus against which the player (statically) applies force. This can also be
undertaken using a force platform in a squat rack or other rigid structure for
static actions performed standing: measuring the force applied to the ground
through the feet (Wilson and Murphy 1996). In either case the defining aspect
of isometric assessment is that force is applied against immovable apparatus
and that there is no change in joint angle (Abernethy et al. 1995). By
definition, isometric assessment measures strength qualities under static
conditions, hence it provides little information regarding concentric or
eccentric strength capabilities. Measurements with this form of assessment
also vary considerably with changes in joint angle.
Isokinetic strength
Isokinetic assessment uses a dynamometer to control the velocity of
movement while the subject exerts maximal force against the moving lever
arm. These assessments therefore typically involve open kinetic chain
movement – that is, the limb(s) applying force is moving. A common example
of isokinetic strength assessment involves knee extension and/or flexion,
performed seated with the subject’s torso and other limbs secured in place.
This mode of testing assesses the players’ ability to generate torque through a
fixed range of motion for a restricted single-joint movement at a constant
angular velocity (Abernethy et al. 1995). The controlled conditions under
which isokinetic strength measures are recorded assist in producing reliable
(that is, repeatable) measurements. Conversely, the controlled and restricted
nature of isokinetic dynamometry renders this mode of strength assessment
less applicable to athletic movements. In most sports, strength is expressed
during movements that are commonly performed in a weight-bearing posture
(not performed seated) and involve complex rather than single-joint actions.
In accordance with this, isokinetic strength measures are typically not
reported to be sensitive to changes in measures of athletic performance
(Murphy and Wilson 1997).
Isoinertial strength
Isoinertial strength assessment employs free weights or fixed resistance
machines to quantify the greatest resistance the player can lift for a specified
range of motion. Common machine-based assessments include leg press, chest
press or shoulder press fixed resistance machines. Strength assessment
involving fixed resistance machines share similar issues of biomechanical
specificity to those described for isokinetic testing. Isoinertial strength
assessment that employs free weight resistance is therefore the preferred
method of assessment for athletic populations. This form of testing typically
involves maximal efforts with one of the powerlifting competition lifts: barbell
squat, deadlift and bench press. Isoinertial testing with free weights allows
strength to be assessed for weight-bearing tasks, including closed kinetic chain
movements, and also features the coupling of eccentric and concentric actions.
Furthermore, these tests require the player to balance both themselves and the
resistance whilst generating force, as opposed to having the plane of
movement fixed and the body supported in a sitting or lying position, as
occurs during fixed resistance machine assessments.
As such, isoinertial assessment with free weights is considered the testing
mode that bears closest resemblance to what occurs during athletic
movements (Newton and Dugan 2002). By definition, players’ isoinertial test
scores will to some extent be limited by their level of skill in performing the
given strength exercise movement (Abernethy et al. 1995). However, such
issues will likewise influence a player’s ability to express their strength
capabilities during sports skill and athletic movements.
Repetition maximum (RM) testing is widely used in physical assessment in
sports: a player’s one-repetition maximum (1-RM) for a particular lift is
defined as the highest weight they are able to lift for one repetition through
the full range of motion of that lift (Morales and Sobonya 1996; Harman and
Pandorf 2000). In terms of practicality, 1-RM testing can be carried out in the
weights room as it does not require specialised equipment and so can be
undertaken at the team’s training facility. Free weights 1-RM testing does
demand a level of technical competence. From a safety viewpoint it is
important that lifting form and posture does not break down under the
maximal loads used, particularly in the case of barbell squat and deadlift.
An alternative to one-repetition maximum (1-RM) testing that attempts to
avoid such issues involves the use of submaximal strength testing at lower
repetition maximum loads, from which 1-RM values can be predicted
(Morales and Sobonya 1996). One such approach is to assess the maximum
load the player can lift for a specified number of repetitions, for example 3RM or 5-RM testing. The number of repetitions chosen for submaximal RM
testing influences the accuracy of the 1-RM prediction. The submaximal
repetition test that most closely predicts 1-RM load reportedly also appears to
vary according to the lift. A study of collegiate power athletes (football
players and athletics field event throwing athletes) identified that 95 per cent
1-RM loads best predicted 1-RM values for bench press, which equates to a 2RM test (Morales and Sobonya 1996). In contrast, the best prediction for power
clean lifts were made at 90 per cent 1-RM (equating to a 4-RM test), whereas
for barbell back squat the best prediction was made using 80 per cent 1-RM (8RM test) in these athletes.
Assessing eccentric strength
Assessment of eccentric strength has traditionally been undertaken using
isokinetic devices; that is, the player resists with maximal force the movement
of the lever arm of the dynamometer as it moves in the opposite direction at a
set angular velocity. This mode of eccentric strength testing carries the same
biomechanical and postural specificity issues as described for concentric
isokinetic strength assessment. Isoinertial assessments of eccentric strength do
also exist, although they are not currently widely used (Meylan et al. 2008).
Assessments of this type include protocols employing variations of standard
strength exercises that impose a 3-second eccentric phase; that is, evaluating
the maximum weight the subject is capable of lowering for a duration of three
seconds through the full eccentric range of motion for the particular lift. Other
forms of isoinertial eccentric-strength assessment employ a force platform and
measure ground reaction forces during high-load or high-velocity eccentric
movements. The use of these latter protocols will be restricted by access to the
force platform equipment required and availability of trained staff to operate
the apparatus.
Maximum force developed under eccentric (lengthening) conditions will
always exceed maximum voluntary force developed during concentric or
isometric contractions. As such the loads involved during eccentric strength
testing exceed those used during isometric or concentric strength testing
(Meylan et al. 2008). The higher level of loading imposed raises concerns over
the safety of this form of assessment for some players. This is particularly the
case with young players who are still maturing physically, and conversely
older players who also may not tolerate the physical stresses involved.
Strength-endurance
Strength-endurance is identified as an independent aspect of neuromuscular
performance, as opposed to just a derivative of other strength properties
(Yessis 1994). This capability is commonly assessed by evaluating the number
of repetitions the player is capable of completing at a given submaximal load.
The load used is usually set as a percentage of their 1-RM for the particular
strength exercise or body weight (for example, maximum chin up test). The
number of repetitions through the full range of motion the player is able to
complete with the predetermined load is then used as the outcome measure.
One notable example of a commonly administered strength-endurance test
is the 225lb bench press repetition test that is performed as part of the NFL
Combine. This is categorised as a test of strength-endurance for these
American football players on the basis that the average number of repetitions
completed by eligible players tested in the NFL Combine is reported to be 10
repetitions or above (Sierer et al. 2008). This may not be the case for other
players in other sports, however.
Assessing ‘speed-strength’ or explosive power
Testimony to the high perceived importance of ‘explosive’ power or speedstrength with respect to sports performance (Abernethy et al. 1995), numerous
different testing modalities exist to assess this particular quality.
Isokinetic dynamometry
Isokinetic testing using higher angular velocities on the dynamometer have
been used as a measure of both high-velocity strength and speed-strength. In
the same way as discussed for strength assessment, the validity of this form of
testing for evaluating speed-strength performance is questionable. Isokinetic
measures of speed-strength, in the form of hamstring and quadriceps torques,
show no relation to sprint times over any distance (5m, 10m, or 30m) in team
sports players (professional and semi-professional rugby league players)
(Cronin and Hansen 2005). This finding is in keeping with the lack of
biomechanical specificity with respect to the co-ordinated multi-joint
movements that feature in athletic performance of the single-joint open
kinetic chain movements involved in this form of assessment.
Tests of rate of force development
Rate of force development (RFD) is identified as a key component of speedstrength performance (Newton and Kraemer 1994). However, in accordance
with test specificity, the conditions under which this aspect of neuromuscular
function is measured have a major bearing on its validity. When measured
under isometric (static) conditions, RFD scores showed no change in response
to either ballistic, plyometric or strength-oriented lower-body training, even
though improvements were demonstrated in measures of dynamic athletic
performance (Wilson et al. 1993). A concentric measure of RFD was, however,
shown to be capable of discriminating between good and poor performers on
a sprint test, where the isometric RFD test failed to do so (Wilson et al. 1995).
The measure of RFD selected is shown to be important in terms of
reliability. Specifically, peak RFD values are subject to a high degree of
random error as it represents a single point on the force–time curve, whereas
mean RFD is a far more reliable and robust measure as it is derived via
integration of the whole of the force–time curve. Measurement of RFD does
also require expensive and not easily portable equipment: typically a force
plate. For these reasons, assessments of this type tend to share the same issues
of cost and practicality as other forms of laboratory-based testing.
Isoinertial assessment of power output
Isoinertial assessments of power output against resistance loads have typically
employed apparatus such as a Smith machine that consists of a barbell
mounted on vertical runners. In this way, isoinertial resisted movements can
be performed, albeit in a single vertical plane, and position transducers built
into the device can be used to quantify barbell velocity and acceleration;
hence mechanical power output can be derived via the following formula:
P = force (barbell mass × acceleration) × velocity
The barbell jump squat is most commonly employed for isoinertial
assessment; however, the barbell bench throw has also been used to evaluate
upper-body power expression. The barbell bench throw does, however,
require either specialised apparatus or spotters to assist with catching the bar
after it has been projected to avoid endangering the athlete.
Assessment of maximal power Pmax load
Much attention has been given to the load at which peak power output is
achieved, termed Pmax from both a training and testing viewpoint. Athletes’
power outputs across a spectrum of loads for a ballistic speed-strength
exercise (typically barbell jump squat or bench throw) have been used to
identify both this Pmax value and athletes’ power output curves (plotted
against load) (Harris et al. 2007). Similarly, an increasingly common practice
when testing an athlete’s speed-strength capabilities is to plot their individual
load versus power output curve for the jump squat. One proposed application
of this method is to serve as a diagnostic tool to guide athletes’ training
prescription in order to shift their load/power curve in a certain direction.
However, it has been highlighted that the apparatus (Cormie et al. 2007a)
and method of calculation (Cormie et al. 2007b) commonly employed in fact
produce grossly inaccurate power output values. This results in a warped load
versus power output plot, which is not reflective of the true relationship
(Cormie et al. 2007b). When the correct apparatus is employed and power
output values are calculated correctly it has been shown that the load which
maximises power output for the barbell jump squat in fact equates to zero per
cent 1-RM: that is, the player’s own body mass without any external load.
This result has been reported for both adolescent (Dayne et al. 2011) and
college-aged male athlete subjects (Cormie et al. 2007b).
Furthermore, a number of authors increasingly question the practical
importance of this Pmax value, and such application of the load/power output
curve is also debated. A study of senior elite rugby union players reported that
the difference in power outputs either side of the calculated Pmax value were
minimal: loads 10 per cent and 20 per cent above or below the player’s
identified Pmax load on average affected power outputs by only 1.4 per cent
and 5.4 per cent respectively (Harris et al. 2007). In terms of practical
application, Pmax values also appear to relate only to the training movement
tested and thus cannot be generalised to other training exercises.
Jump squat testing
As discussed above, jump squat assessments of speed-strength performance
are often conducted over a range of loads. From a methodological point of
view, it appears that the use of apparatus such as a Smith machine may
impact upon the relationship between jump squat power output and measures
of athletic performance (Cronin and Hansen 2005). Scores on an unrestricted
squat jump using a free weight Olympic barbell were found to correlate with
sprint performance in rugby league football players (Cronin and Hansen
2005), whereas absolute squat jump scores measured in restricted apparatus
reportedly did not (Baker and Nance 1999a). By restricting the plane of motion
of the bar it may be that this apparatus affects the functionality of the test by
reducing the degree of specificity to sports movements, such as balance and
co-ordination aspects (Cronin and Hansen 2005).
Devices are now commercially available that allow free weight barbell
jump squats to be used for the same form of assessment to evaluate power
output. However, preliminary data indicate that these accelerometer
apparatuses may not provide accurate values for peak velocity or power when
performing unrestricted jumping movements (McMaster et al. 2011). These
findings are in support of a previous study which reported systematic bias and
large random error in measurement of peak power and peak force with
commercially available accelerometer and linear position transducer devices
(Crewther et al. 2011). It also appears that measurements are affected by
where the accelerometer device is mounted: that is, whether it is affixed to the
athlete or on the barbell. The greatest accuracy of measurement seems to be
associated with peak force values derived when the device is mounted directly
on the hip of the athlete (McMaster et al. 2011).
Olympic weightlifting repetition-maximum testing
Another common measure of speed-strength capabilities against greater
resistance involves repetition-maximum (RM) testing using Olympic
weightlifting movements. The power clean is generally chosen due to the
familiarity of this lift for most players and the fact that it has a distinct end
point – essentially the player either fails or succeeds to catch the bar at the top
of the lift. In much the same way as for free weight isoinertial strength tests,
players’ scores will tend to be limited by their technical proficiency with the
lift. To avoid such limiting factors, some practitioners employ the pulling
derivatives of the Olympic lifts for RM assessments: that is, without the catch
portion of the movement at the top of the lift. This may help to offset issues
relating to lifting skill associated with the ‘catch’. However, there may be
other issues using the Olympic pulling derivatives for RM testing. In the
absence of the catch as a distinct end point, there are challenges standardising
how high the barbell must be raised in order to deem that the player has
successfully completed the pulling lift with a given weight.
Repetition-maximum testing using the hang power clean (that is, a power
clean initiated with the bar at the ‘hang’ position at mid-thigh) is also often
used to assess maximum speed-strength capabilities. Australian rules football
players’ scores on the 1-RM hang power clean were found to be related to
their vertical jump, maximum strength (squat 1-RM) and sprint performance
(Hori et al. 2008). Similarly, the power clean 1-RM scores of college American
football players, expressed relative to body mass, were reported to show a
significant statistical relationship with measures of acceleration and straightline sprint performance (Brechue et al. 2010).
Vertical jump assessment
Variations of the vertical jump are the most commonly employed measure of
lower-body ‘explosive power’ or speed-strength performance for both athletic
and non-athletic populations (Klavora 2000). Some have questioned the
validity of using vertical jump as a specific measure of lower-body power
given that multiple segments, including both lower and upper limbs,
contribute to the movement and that motor skill and co-ordination aspects
also influence vertical-jump performance (Young et al. 2001b). Regardless of
these debates, from the point of view of assessing athletic performance the
vertical jump is a common action in most sports and is biomechanically
similar to various acceleration and game-related dynamic movements. It
would therefore appear valid to include some form of vertical-jump
assessment in a battery of tests to assess speed-strength expression and
athletic performance of team sports players.
The standard test for concentric power production is the squat jump,
executed from a set squat depth, and initiated without any countermovement.
The countermovement jump, with eccentric and concentric movements
performed rapidly and without a pause, is the standard test of combined
concentric and ‘slow’ stretch-shortening cycle performance. The difference
between (concentric-only) squat jump and countermovement jump height has
been used to evaluate the contribution of the eccentric phase or ‘slow’ stretchshortening cycle to the player’s performance. Drop vertical jumps may also be
used in a similar way to evaluate the ‘fast’ stretch-shortening cycle
component (Ford et al. 2005); this form of assessment does, however, also
comprise reactive strength qualities (discussed in the following section).
One study reported that of a range of field-based vertical jump tests the
squat (concentriconly) and countermovement jump tests executed with hands
on hips had the greatest reliability with recreationally active subjects (physical
education students), in terms of producing consistent scores across trials
(Markovic et al. 2004). However, restricting the use of arm swing would
appear to compromise the biomechanical specificity of the jump movement –
very few jumping movements in sport are executed without using the arms.
Removing arm swing also has the effect of reducing jump height (in
comparison to the corresponding test performed with arm swing) (Feltner et
al. 1999; Markovic et al. 2004). Arm swing is shown to augment torque
generation at hip and knee joints during the propulsive phase of the vertical
jump (Feltner et al. 1999). Another related methodological consideration is
that jumping (with arm swing) to reach a target overhead has been shown to
influence both movement mechanics and jump height (Ford et al. 2005). It
follows that an overhead goal should be a feature of the field test apparatus
used to measure jump height where possible – and that arm swing (and reach)
should be permitted during the test movement.
In accordance with the methodological and specificity considerations
discussed, a field testing device using a jump and reach protocol (with arm
swing and reaching up to touch measurement vanes positioned overhead) was
reported to have the highest correlation with selection in a sample of elite ice
hockey players (Burr et al. 2007). This study examined both squat (concentriconly) and countermovement jumps and compared correlations with the
respective tests performed using a contact mat system and performed without
arm swing. Jump and reach scores using the overhead measuring vane
apparatus correlated more closely with the order of players’ eventual order of
selection in the National Hockey League draft than the corresponding squat
and countermovement jump (no arm swing) scores on the contact mat system
(Burr et al. 2007). The authors of this study concluded that the overhead
measurement vane apparatus using a jump and reach protocol – in particular
the concentric-only squat jump and reach – was the most appropriate for office testing for elite ice hockey players.
It has been shown that a one-step initiation movement before executing a
(bilateral) countermovement jump increases jump height (Lawson et al. 2006).
The one-step lead in technique also alters the biomechanics and kinematics of
the movement (joint angles and ground reaction forces) despite the fact that
the jump is still executed from two legs (bilateral stance). A study of male and
female volleyball players found that players preloaded their lead leg during
the step close version of the test, resulting in greater hip, knee and ankle
torques and ground reaction forces measured in lead leg versus trail leg
(Lawson et al. 2006). Assessing both dominant and non-dominant leg as the
lead leg during step close jumps can also indicate bilateral differences in
performance between lower limbs. Single-leg variations of the standard
vertical jump tests can be used in the same way (Newton et al. 2006).
Likewise, vertical jumps with run-up of various distances (1-step, 3-step, 5step) have also been used to assess power and athletic performance (Young et
al. 2001b).
Horizontal jump tests
Standing long jump and standing triple jump are also used to measure lowerbody power in a horizontal movement, in contrast to most forms of
assessment which evaluate only movement in a vertical direction. The fact
that horizontal jump tests require generation of horizontal and vertical ground
reaction forces is identified as beneficial in terms of replicating running and
locomotion activities that feature in sport (Holm et al. 2008). The greater
specificity of this mode of assessment is reflected in positive statistical
relationships reported with measures of acceleration, speed and change of
direction (Brughelli et al. 2008; Peterson et al. 2006). The single-leg
countermovement horizontal jump in particular is identified as a good
predictor of speed and change of direction performance (Meylan et al. 2009).
In addition to strength and power qualities of the locomotor muscles, this
form of assessment also demands co-ordination and balance, particularly
when the test involves multiple jumps, hops or bounds (Hamilton et al. 2008).
Consequently, one methodological consideration with these horizontal jump
tests is that subjects’ familiarity with the movement will tend to influence the
reliability of scores between trials (Markovic et al. 2004). Specifically, a motor
learning effect has been observed with physical education students during a
single test session – so that performance tended to improve with consecutive
trials (Markovic et al. 2004). For this reason practice trials are recommended
prior to assessing performance, particularly during the initial stages when
these tests are first introduced.
Assessing reactive (speed-)strength and stretchshortening cycle performance
Reactive strength concerns the coupling of eccentric and concentric muscle
actions; this form of assessment typically requires the athlete to decelerate
their own momentum in a negative direction, before reversing the movement
to initiate a concentric propulsion action in a positive direction (Newton and
Dugan 2002). As such, these measures comprise both eccentric and concentric
speed-strength qualities, in addition to stretch-shortening cycle (SSC)
components. Assessment of reactive strength for ‘slow’ SSC movements that
feature longer ground contact are derived from the difference between
concentric-only jumping measures (for example, squat jump) and
countermovement jump height. Lower limb reactive strength and fast SSC
performance are typically assessed via drop jump testing. Drop jump height is
also often expressed with respect to the player’s corresponding
countermovement jump height score. When conducting drop jump tests to
measure reactive strength, participants are instructed to maximise jump
height whilst minimising the time in contact with the ground – so that the
participant aims to initiate the jump as soon as they touch down after
dropping down from the box.
If drop tests are carried out using a force platform or contact mat, a
‘reactive strength index’ can also be derived from the ratio between contact
time and flight time (elapsed time between take-off and landing) (Newton and
Dugan 2002). The validity of the drop jump height measure is supported by
the observation that drop jump height index scores correlated with sprint
performance in female high school sprinters (Hennessy and Kilty 2001). This
form of assessment often involves multiple drop jumps executed from various
box heights: drop height can then be plotted against heights jumped to
provide a profile of the player’s drop jump and fast SSC reactive strength
capabilities. Players with a plyometric training background will tend to jump
higher from a drop jump – so that the box height used in training can be
increased until they reach a drop jump height that exceeds their fast SSC
reactive strength capabilities. A study assessing athletes from different sports
using a drop jump test from a relatively large height (60cm) showed that team
sports (soccer, volleyball, handball and basketball) players employed different
motor strategies to track and field athletes and rowers when performing the
drop jump test (Kollias et al. 2004). Like other types of jump, the presence of a
vertical goal during vertical drop jump testing appears to influence movement
mechanics, lower limb biomechanics, contact time and even jump height
(Ford et al. 2005).
Single-leg variations of the vertical jump test also exist which allow the
reactive speed-strength and SSC performance of dominant and non-dominant
limbs to be assessed independently. Likewise, horizontal drop jump tests have
also been investigated (Holm et al. 2008). These tests involve dropping
(vertically) from a box of specified height and immediately jumping for
distance in a horizontal direction upon touchdown. Horizontal drop jump
testing also includes both bilateral and unilateral variations. The single-leg
horizontal drop jump test has reported positive statistical relationships with
measures of acceleration and speed performance with team sports players
(Holm et al. 2008).
Triple-hop testing offers another means to assess reactive speed-strength
performance in a horizontal direction (Hamilton et al. 2008). In addition to
reactive speed-strength and stretch-shortening cycle qualities, executing
repeated hops requires considerable athleticism, balance and postural stability.
Triple jump or hop performance is therefore likely to demonstrate a marked
familiarisation effect (Markovic et al. 2004). Performance on the triple hop test
was shown to be related to vertical jump performance in male and female
collegiate soccer players, which led the authors of this study to conclude that
the triple hop test was a valid measure of power performance in these players
(Hamilton et al. 2008). The unilateral nature of repeated hop tests allows
comparison of performance between limbs. A five-hop variation of this test
was shown to identify differences in performance between dominant and nondominant limbs among collegiate female softball players (Newton et al. 2006).
Accordingly, single-leg repeated hop tests of this type have seen application in
a rehabilitation setting to evaluate functional performance of injured versus
uninjured legs (Hamilton et al. 2008).
Evaluating endurance performance
One approach when assessing endurance capabilities of athletes is to test the
individual physiological parameters that underpin endurance performance
(Jones and Carter 2000). Traditionally, the standard measure of endurance
capacity has been the measured maximal oxygen uptake or VO2max, which is
typically evaluated in the laboratory using a variety of incremental test
protocols performed to failure. The running velocity or work intensity at
which VO2max is attained (also known as ‘vVO2max’) can also be used as an
index of aerobic endurance capacity. This parameter has traditionally been
assessed using laboratory protocols with direct measurement of expired air.
Other approaches to assessing vVO2max or maximal aerobic speed (MAS)
evaluate this parameter using a maximal incremental test performed to
volitional failure; these protocols may or may not record oxygen uptake or
heart rate given that vVO2max or MAS is the criterion measure. These
protocols were originally devised to be performed on a running track (Leger
and Boucher 1980); however, shuttle-running based field test protocols that
allow an analogue measure of MAS to be derived have also since been
developed for application with team sports players.
In addition to maximal oxygen uptake, a player’s aerobic endurance is also
determined by their capacity to sustain a high percentage of their maximum
aerobic output without lactate accumulation. This parameter is termed the
lactate threshold (LT) or maximum lactate steady state (MLSS), and is in turn
linked to the athlete’s muscle buffering capacity as well as their propensity to
metabolise and clear lactate. Similarly, given the intermittent nature of
activity team sports, anaerobic capacity and repeated sprint ability are also
critical factors that determine sport-specific endurance capacities. The final
factors that contribute to endurance performance are running economy or
work efficiency. This can be viewed as the neuromuscular component of
endurance. In the context of team sports, it follows that any test should aim to
replicate the types of locomotion that features during a game in order to fully
address this movement economy factor when assessing aerobic endurance
(Aziz et al. 2005).
Laboratory assessments
Laboratory testing requires specialised equipment that is expensive and
requires trained personnel to operate it. Given these cost issues, as well as the
time demands of testing each player individually, laboratory testing is not
generally amenable to application with squads of players (Impellizzeri et al.
2005). In the case of intermittent sports, and particularly team sports, the use
of laboratory-based assessment is therefore typically restricted to a research
setting. In addition to these issues of practicality, the validity of laboratorybased measures that are typically derived from continuous protocols
performed on a treadmill has also been questioned for team sports players
(Carey et al. 2007).
Field tests have therefore been developed that offer a more practical and
potentially more valid alternative for use with players who compete in
intermittent sports. As the field-test protocols are often closer to what occurs
in intermittent sports, these tests are often considered more relevant to players
and coaches in these sports than laboratory tests (Bosquet et al. 2002). Scores
with these field tests generally report high correlations with laboratory test
measurements (Bosquet et al. 2002). Regression equations do also exist that
can be used to derive estimated scores for standard ‘laboratory’ measures,
such as VO2max (Impellizzeri et al. 2005).
Field-based maximal tests of cardiorespiratory fitness
Incremental protocols for over-ground running
Protocols such as the Université de Montréal track test were originally devised
for over-ground running on a running track in order to assess athletes’
vVO2max, and thereby provide an indirect estimate of maximal aerobic
capacity without direct measurement of expired air (Leger and Boucher 1980).
However, a strong relationship has emerged between vVO2max and
endurance performance in competition, so that vVO2max has to some extent
replaced VO2max as the criterion measure. In recent years a modified version
of the original Université de Montréal track test has been developed, named
the Vam-eval protocol. This test is performed on a running track and the pace
is controlled using audio signals: the starting velocity is 8ms–1 and running
speed is increased by 0.5ms–1 each minute (Chtara et al. 2005).
Measures of vVO2max and MAS have been identified as key parameters of
endurance for team sports players. Despite this, vVO2 scores derived from the
Vam-eval incremental track test protocol were not reported to correlate well
with running performance recorded during a match for the majority of
playing positions in youth soccer (Buchheit et al. 2010c). This lack of
relationship may be a consequence of the lack of specificity of this mode of
assessment; continuous running around a track is not reflective of the
intermittent nature of exertion or the frequent changes in direction that occur
during a match.
Twenty-metre multistage shuttle test
In order to improve the specificity of assessment modes, various shuttle run
protocols have been developed for use with team sports players (Castagna et
al. 2006). The 20m multistage fitness test has become a standard field test for
aerobic endurance (Flouris et al. 2005; Wilkinson et al. 1999). Measured
VO2max during the 20m multistage shuttle test (MST) has shown to
correspond well with laboratory measured VO2max during a maximal
treadmill test for team sports players (rugby players and field hockey players)
(Aziz et al. 2005). The fact that endurance athletes (triathletes and runners)
showed different VO2max scores between the field and treadmill tests points
to the greater familiarity and specificity of the shuttle run test mode for team
sports players as opposed to endurance athletes.
The 20m MST has been adapted for other sports: an on-ice version of the
test was devised and validated for ice hockey players (Leger et al. 1979).
Variations of the original 20m MST have also been proposed. These include a
modified incremental 20m shuttle test that increases running speed after each
shuttle (Wilkinson et al. 1999), as opposed to increasing velocity at 1-minute
intervals as occurs with the original version of the test. The authors of this
study argue that such an approach avoids the tendency for players to drop out
at the start of a given level, as can happen with the original test protocol
(Wilkinson et al. 1999). Such a scenario may make the original 20m MST less
sensitive to changes in training status, as players may voluntarily drop out
once they have achieved their target level rather than continuing to volitional
fatigue.
Yo-Yo intermittent test
Other field tests of aerobic endurance that are widely used in team sports
include the Yo-Yo intermittent fitness test, which has become particularly
popular in soccer (Metaxas et al. 2005). The most striking feature of the Yo-Yo
intermittent test protocol is that players do not run continuously. The test
requires subjects to perform repeated bouts of running (two sets of 20m
shuttle runs) at increasing intensity; these work intervals are interspersed with
10-second rest periods (Bangsbo et al. 2008). A correlation study concluded
that, although the two measures were correlated, this intermittent test
protocol assessed physiological qualities additional to the continuous 20m
shuttle test (Castagna et al. 2006). The Yo-Yo intermittent test protocol would
appear to more closely resemble the intermittent nature of exertion that
players engage in during competition. Two versions of the Yo-Yo intermittent
test protocol exist: Yo-Yo intermittent recovery level 1 (IR1) begins at a slower
running velocity and so features more progressive increases in running speed;
level 2 (IR2) starts at a faster velocity so that subjects engage in high-intensity
exertion much sooner (Bangsbo et al. 2008). Both versions of the test have
been found to have acceptably high levels of test–retest reliability with
various groups of subjects.
Regression equations also exist to predict VO2max from both IR1 and IR2
Yo-Yo test performance. However, some studies have found that the Yo-Yo
intermittent field test offers a less accurate measure of VO2max than
laboratory-based treadmill tests that directly measure oxygen consumption
(Metaxas et al. 2005). From a practical viewpoint it should be borne in mind
that obtaining a measure of VO2max is of less relative importance than
providing an assessment of the endurance capacity of players competing in
intermittent sports, which will inevitably feature an anaerobic component.
In support of this, a study of Australian rules football reported that players’
VO2max scores showed no difference between starting players and substitutes,
whereas Yo-Yo IR2 test scores were able to differentiate between starting and
non-starting players (Young et al. 2005). Another study, this time in soccer,
found that Yo-Yo IR1 test scores recorded by soccer players were shown to
correlate to their on-field performance (quantity of high-intensity running
total undertaken during games), whereas their treadmill VO2max scores did
not (Krustrup et al. 2003). These studies indicate that it is beneficial for field
tests of endurance to feature an anaerobic component in order to be reflective
of the specific endurance capabilities required by intermittent sports.
Accordingly, scores on the Yo-Yo IR1 test reported positive statistical
relationships with a variety of physical performance measures recorded by
elite youth soccer players during a match (Castagna et al. 2010).
The Yo-Yo intermittent recovery level 2 (IR2) protocol is intended for use
specifically by trained athletes: it is run at faster cadence – hence test duration
is shorter – and is demonstrated to have a large anaerobic component based
upon lactate profiles and muscle biopsy samples (Bangsbo et al. 2008). For this
reason it has been suggested that the IR2 protocol has greater scope for
discriminating between elite players and those competing at lower levels,
given the greater demand for high-intensity exertion during matches at elite
level. Crucially, both IR1 and IR2 tests also appear sensitive to changes in
fitness elicited by training and associated improvements in on-field
performance (time spent engaged in high-intensity running and maximum
distance covered in five-minute interval during a match) (Bangsbo et al. 2008).
30–15 intermittent fitness test
The 20m multistage shuttle run test and Yo-Yo test described previously can
be used to provide an indirect measure of the (shuttle) running speed
associated with VO2max or maximum aerobic speed (MAS). It has, however,
been identified that the values provided by the Yo-Yo test particularly do not
correlate well with direct measures of MAS or vVO2max and therefore it has
been argued that the Yo-Yo test scores should not be used for prescribing
training intensity. An alternative protocol, the 30–15 intermittent fitness test
(30–15IFT), has been developed specifically for the purpose of evaluating an
analogue measure of MAS in the field.
The measure derived from the final running speed achieved in this protocol,
termed VIFT, in fact equates to an intensity above vVO2max. Typically, VIFT
scores are ≈20 per cent higher than MAS scores from a continuous overground running test, such as the Vam-eval, and ≈35 per cent higher than the
final shuttle running speed recorded on the 20m MST (Buchheit 2008). Players’
VIFT scores do, however, correlate well with both these measures.
Furthermore, due to the reliability and accuracy of the VIFT measure for
individualising players’ training intensity, the 30–15IFT protocol is becoming
widely used when undertaking interval running conditioning in team sports
(Buchheit 2008).
The 30–15IFT protocol is intermittent in nature, in a similar way to the YoYo test. Subjects run shuttles for 30 seconds at a given velocity interspersed
with 15 seconds active recovery bouts; running velocity for the work bouts is
progressively increased with each run. However, the course consists of two
cones spaced 40 metres apart: subjects perform an initial 40m run, followed by
a 180-degree turn and a run of a specified distance in the opposite direction.
The calculated distances for each run are corrected for the time required to
complete the necessary 180-degree turns (Buchheit 2008). During the later
levels when the pace increases and the distance for the return shuttle exceeds
40m, the player makes a final 180-degree turn and runs a specified distance in
the original direction. The 30–15IFT has been validated against vVO2max
directly measured in the laboratory and MAS measures derived from standard
field tests involving continuous over-ground running. Scores on the 30–15IFT
also correlated well with other tests of speed (10m sprint) and power (vertical)
in young team sports players (Buchheit 2008). An on-ice version of the 30–
15IFT has also recently been developed and validated for ice hockey players
(Buchheit et al. 2011b).
Sport-specific test protocols
An alternative approach to assessing endurance performance for sports is to
test players’ scores on specific tests designed to replicate the endurance
demands of the sport (Hoff 2005; Impellizzeri et al. 2005). Both treadmill
(laboratory-based) (Sirotic and Coutts 2007) and field-based (Hoff 2005) sportspecific endurance tests of this type have been developed. Such tests aim to
simulate movement patterns and even incorporate technical skills that feature
in the sport in order to increase the level of specificity of the test measure
(Impellizzeri et al. 2005). The integrated approach used by such sport-specific
protocols thus attempts to assess endurance performance in a way that
reproduces the bioenergetics of the sport. As such, these tests do not offer
insight into individual physiological components; rather energy systems and
performance abilities are assessed in combination (Impellizzeri et al. 2005).
However, serious limitations to this approach exist. One major issue is the
difficulty in standardising conditions in order to obtain a reliable and
repeatable test measure. Similarly, the challenge with these sport-specific test
protocols is accumulating sufficient normative data to provide reference
values against which to evaluate players’ scores. In the case of treadmill
‘sport-specific’ simulations, the usual practical issues with regard to
laboratory-based testing for large numbers of players also arise.
Submaximal tests of endurance fitness
When performing serial measurements with players, repeated use of maximal
tests may engender motivation and compliance issues. Progressive tests to
exhaustion are dependent upon the motivation of players to perform
maximally (Lemmink et al. 2004). In view of this, attention has been given to
submaximal tests for endurance performance. Submaximal tests would seem
to be more conducive to repeated testing at regular intervals given that they
avoid such complications with respect to motivation and compliance
(Impellizzeri et al. 2005; Krustrup et al. 2003; Lemmink et al. 2004).
Such submaximal tests are often modified versions of existing progressive
maximal test protocols; essentially the test is terminated at a predetermined
submaximal workload. The test scores recorded are generally based upon
measurement of physiological responses (for example, heart rate) during
and/or following the standardised final (submaximal) workload (Lemnink et
al. 2004). In the laboratory ventilatory and heart rate responses can be
recorded to provide a measure of how taxing the submaximal workload was
for the player on a given test occasion. A notable example of an equivalent
field-based test is the submaximal ‘non-exhaustive’ version of the Yo-Yo test
of aerobic fitness (Bangsbo et al. 2008). The protocol used is identical to the
maximal version of the test – up until the point when it is terminated ‘early’
at a submaximal workload. One practical issue with field-based submaximal
tests is that these tests do still require that physiological responses (typically
heart rate) are monitored – consequently all participating players must have
access to relevant equipment, such as heart rate monitors (Krustrup et al.
2003).
It appears that submaximal test protocols must exceed a minimum
threshold duration in order to ensure that the outcome measure does show the
desired relationship with maximal performance. A 3-minute submaximal
version of the Yo-Yo test was reported to be insufficient, whereas a 6-minute
protocol did show correlation to maximal Yo-Yo test scores (Bangsbo et al.
2008). Similarly, the data suggest that the higher the final workload (running
speed) chosen for the final stage of the submaximal test the greater the
reliability of the physiological measure, particularly in the case of heart rate
(Lemmink et al. 2004). It has been identified that the final workload should
aim to elicit exercise intensities in the range 86–93 per cent of players’ HRmax
in order to reduce measurement error and improve sensitivity in detecting
meaningful changes (Lamberts et al. 2011). This final test workload might be
determined via baseline testing for the squad of players; however, for
consistency the protocol would thereafter need to remain the same for the
duration of a season of testing. As these tests involve serial measurements,
each player essentially acts as his/her own reference against which scores are
evaluated.
Assessment of running economy or work efficiency
Exercise economy is typically assessed as the oxygen uptake (VO2) at a given
work intensity (Jones and Carter 2000). Running economy is therefore
commonly assessed in the laboratory by measuring the athlete’s oxygen
uptake at a reference running velocity on the treadmill. Similarly, gas analysis
can be used in the same way with cycle or rowing ergometer at a reference
work intensity to evaluate the same parameter for cycling or rowing
performance. Portable gas analysis equipment does exist that can allow
similar assessments to be made in the field, implementing appropriate pacing
on the track to standardise velocity; however, this tends to be less widely
used. Running economy and work efficiency measures will be highly specific
to both the mode (Millet et al. 2002a) and velocity of locomotion (Jones and
Carter 2000) used in testing. Measuring work economy for team sports players
would therefore require that both the different modes and velocities of
locomotion that feature in a game are accounted for. To date no such protocol
exists for team sports players.
Assessments of lactate-handling capacity
Although lactate-handling capacity may be relevant to endurance
performance with team sports players, the measure used to assess this
parameter has a major bearing in terms of comparing players’ scores.
Classically, the criterion for ‘onset of blood lactate’ (OBLA) or lactate
threshold (LT) has been a fixed concentration of blood lactate, typically
4mmol/l (Bosquet et al. 2002). Deflection point(s) in the curve between
running velocity and measured blood lactate are also used as a measure of
lactate threshold. Such tests are typically carried out in the laboratory to allow
running velocity to be standardised and facilitate blood lactate sampling.
Methods for indirect evaluation (without taking blood lactate samples) of
LT or the equivalent ‘anaerobic threshold’ (AT) also exist, which are based
upon changes detected in ventilatory or heart rate responses (Bosquet et al.
2002). The validity of the ‘ventilatory threshold’ (VT) model has been
questioned on the basis that its determination is highly subjective and also
highly variable, as well as being dependent on the criteria chosen. It has also
been demonstrated that the LT and VT can be manipulated independently
under different conditions (Bosquet et al. 2002). Similarly, heart rate-based
procedures are undermined by serious doubts about whether such a
physiological deflection point in heart rate responses actually exists, and if it
does whether it bears any relation to LT (Bosquet et al. 2002).
Lactate threshold
Classically, this lactate threshold has been taken to correspond to a
concentration of blood lactate (BLa) of 4mmol.l–1 – this has been widely used
to denote the ‘onset of blood lactate’ (OBLA). However, over recent years it
has been documented that the actual concentration of BLa that corresponds to
the maximum steady-state workload varies widely between individuals,
falling between a broad range of values from 2mmol.l–1 to 8mmol.l–1 (Billat et
al. 2003). This 4mmol.l–1 OBLA value thus appears to be an arbitrary figure,
which bears little resemblance to the actual BLa concentration at steady state
for many individuals. For the same reasons, comparing absolute values of BLa
concentration sampled within and between studies would also appear
spurious without the appropriate reference MLSS BLa concentration values for
each subject.
Serial measurement of LT has been used to track fitness among junior
professional soccer players via repeated measurements at pre-season and
periodically during the subsequent playing season (McMillan et al. 2005b). The
only significant change in these measures was observed between baseline preseason scores and the in-season test scores – there were no changes
subsequent to the start of the playing season. These serial LT measures were
therefore only sensitive to the gross changes in fitness between pre-season
(which players entered in a relatively detrained state following a five-week
off-season period without structured training) and the start of the playing
season (McMillan et al. 2005b). This apparent lack of sensitivity combined
with the lack of specificity and aforementioned practical issues of laboratory
testing a squad of players, in addition to the methodological concerns
regarding lactate threshold measurement, would seem to call into question the
validity of this form of testing for team sports players.
Maximum lactate steady state assessment
Maximum lactate steady state (MLSS) has been proposed as an alternative
form of assessment of lactate handling for athletes. MLSS is defined as the
maximum intensity at which lactate clearance matches lactate production –
that is, the highest workload that can be sustained without accumulation of
BLa (Billat et al. 2003). From this point of view, MLSS is equivalent to the
theoretical upper lactate threshold at the deflection point in the curve of
lactate concentration plotted against exercise intensity.
Given these methodological and theoretical concerns regarding traditional
lactate threshold measures, the MLSS measure would appear to be a more
robust and valid marker for use as a parameter of endurance performance.
However, determination of MLSS involves a time-consuming protocol
typically involving repeated visits to a laboratory. Direct measurement of
MLSS is also invasive in the sense that it relies upon repeated blood lactate
sampling. Such considerations raise questions about the practicality of
including assessment of MLSS in a standard battery of performance tests for a
squad of players.
Field tests of ‘anaerobic capacity’
The standard measure of anaerobic capacity in the laboratory evaluates
maximally accumulated oxygen deficit (MAOD), which represents the
difference between estimated oxygen demand and measured oxygen uptake
during a maximal exercise test (Moore and Murphy 2003). As discussed
previously, such laboratory-based physiological testing is generally
impractical for routine assessment of team sports players.
Field tests have been developed to assess anaerobic capacity for single
maximal efforts performed at supramaximal intensity. For example, the
Wingate test performed on a cycle ergometer has often been used to assess
anaerobic capacity, based on average power output maintained during the 30second all-out effort (Popadic Gacesa et al. 2009). Fatigue effects observed and
associated decrements in work output are shown to differ between test modes,
and are typically more pronounced for repeated cycling exercise versus
running protocols (Girard et al. 2011a). There is also some question whether
this form of assessment is relevant or valid for running-based sports,
particularly at elite level (Legaz-Arrese et al. 2011).
A running-based protocol that has been reported to correlate well with
MAOD measured in the laboratory involves a maximal 20m shuttle running
test over a total distance of 300 metres (Moore and Murphy 2003). The time
taken to cover this distance is the outcome measure, and typical values
reported are in the range of 62–70 seconds.
Tests of repeated sprint ability
Repeated sprint ability (RSA) is widely recognised as a critical parameter of
endurance for team sports players (Impellizzeri et al. 2008). While measures of
RSA demonstrate moderate statistical relationships with both speed and MST
endurance measures, this capacity is found to be a discrete quality and should
therefore be assessed independently (Pyne et al. 2008). Players’ scores on an
RSA test have reported positive statistical relationships with measures of highintensity running and sprinting distance recorded during matches in soccer
(Rampinini et al. 2007a).
Field-based RSA tests commonly evaluate performance on a series of
maximal efforts. Protocols can be divided into two categories: those which
feature all-out efforts involving relatively longer distance or duration; and
protocols that involve sprint efforts of shorter duration (≤10 seconds) or
distance (generally 40m or less). The majority of test protocols fall into the
former category, with most tests employing sprint bouts of 5–6 seconds
duration or 30–40m in the case of over-ground running protocols. A range of
selected assessments of RSA is presented in Table 2.1.
The rest intervals employed between sprint bouts vary with different
assessments of RSA. This is a factor which strongly influences metabolic and
physiological responses and associated effects on sprint performance in
successive work bouts (Oliver et al. 2009; Spencer et al. 2005). Manifestation of
fatigue effects and any corresponding deterioration in sprint performance
observed also appears to depend to a large degree on the sprint distance or
duration assessed. An investigation by Balsom and colleagues (1992) employed
15 sets of 40m sprints with different recovery intervals (30-secs, 1-min or 2min). The common finding whatever the recovery duration employed was
that 30–40m split times were most consistently affected in the latter sprints
(Balsom et al. 1992). In contrast, the fatigue effects on sprint performances
over shorter distances were less apparent. Indeed, changes in 0–15m split
times were only seen with the shortest 30-second rest interval protocol, and
the decrements in performance were only minor (Balsom et al. 1992).
In order to provide a specific measure of RSA for the sport there is an
argument that sprint distances and rest intervals selected should reflect what
occurs during a match (Bishop et al. 2001). Sprint distances and durations
most commonly observed during matches in field-based team sports equate to
10–20 metres or 2–3 seconds, which contrasts with most RSA assessment
protocols (Spencer et al. 2005). Equally, it could be argued that the distance or
duration of sprint bouts and the duration of rest intervals employed should
represent the extremes of what the player might face during competition, in
order both to provide a sufficiently challenging assessment, and also to ensure
that fatigue effects will be elicited during successive sprints.
Table 2.1 Selected repeated sprint ability test protocols
Assessments of RSA generally provide two different indices of performance:
the sum of all sprint efforts (combined distance covered or sprint times
recorded); and a measure of the relative decrement in performance across
repeated sprint bouts. The way that the latter measure is calculated appears to
be a critical factor (Spencer et al. 2005; Girard et al. 2011a). For example, some
protocols employ a simple fatigue index measure: that is, a percentage score
derived from the calculation:
(best sprint trial score – worst sprint trial score) / best sprint trial score
It is argued that this fatigue index measure generally does not provide a good
measure of repeated sprint ability (Oliver 2009; Pyne et al. 2008; Spencer et al.
2006). Therefore an alternative measure, termed the percentage decrement
score or Sdec, has been recommended as a more valid and reliable measure of
fatigue for repeated sprint ability tests (Glaister et al. 2008). The calculation of
Sdec takes into account performance for all sprint trials in the repeated sprint
test:
Assessing speed components
In the context of team sports, speed comprises the ability to move at high
velocity in a variety of directions, and often not in a straight line; equally
critical is the player’s ability to change direction at pace. Players’ scores on
straight-line sprinting and tests of change of direction performance typically
show only limited statistical relationship. A study of professional soccer
revealed that players’ acceleration, maximum speed and change of direction
test scores shared low statistical relationships (Little and Williams 2005). The
authors concluded that these are distinct and separate abilities: accounting for
the fact that the corresponding scores were relatively unrelated in these
players (Little and Williams 2005). Furthermore, correlations between
measures of these abilities reportedly decrease markedly when any sport skill
component is incorporated in the agility test (Young et al. 2001b). This appears
to reflect the dissimilarity of movement mechanics between straight-line
running and the locomotion employed during change of direction tasks
(Sheppard and Young 2006, Young et al. 2001a).
A number of electronic timing gates systems are commercially available
that offer high degrees of accuracy (to nearest hundredths or thousandths of a
second) and reliability. Such timing gates are amenable to both straight-line
sprinting tests and change of direction tests, and this equipment is also
portable so is suitable for field testing. Access to timing gate devices is almost
a prerequisite if the strength and conditioning specialist aims to conduct speed
or change of direction testing with any confidence, in terms of accuracy and
reliability (Brown et al. 2004). The inaccuracy of results reported when timing
using handheld stopwatches is compounded by the finding that, while
handheld stopwatch-recorded times are generally faster than those recorded
using electronic timing, this is not a consistent outcome (Hetzler et al. 2008).
As a result, it is not possible to apply a correction factor in order to convert
stopwatch-recorded times. Based on these findings, it seems that when testing
is conducted with a handheld stopwatch, the times recorded should be used
only as a guide and the coaches should be made aware of the random
measurement error with this method.
From a context specificity viewpoint, it would appear advantageous that
testing should take place on a similar surface and setting to that upon which
players train and perform (Handford et al. 1997). One caveat for sports that
are played outdoors on a grass surface is that weather and pitch conditions
may vary, which can influence serial measurements over time. From the point
of view of standardisation it may therefore be preferable to use an all-weather
artificial surface or indoor artificial turf facility for field-based running speed
assessments in these outdoor field sports.
Measures of straight-line acceleration abilities
Speed scores over 5m have been employed as a measure of ‘first-step
quickness’ (Cronin and Hansen 2005). Players’ split times over 10m or 15m are
likewise often used to evaluate acceleration ability. Whereas the ‘first-step
quickness’ time over 5m and ‘acceleration’ 10m time correlated closely in
semi-professional and professional rugby league players, their 5m times were
much less closely related to their maximal speed scores over 30m (Cronin and
Hansen 2005). These findings indicate that acceleration and maximal speed are
quite distinct abilities in team sports players, and should therefore be
evaluated as such.
Assessment of straight-line running speed
Assessments of running speed commonly used in team sports typically
employ total distances of 30 or 40 metres, depending largely on the convention
for the sport (Gamble 2011b). In North America it is customary to assess speed
over a distance of 40 yards; for example, the NFL Combine features the 40yard dash (Sierer et al. 2008). In addition, these tests often include split times
over specified distances in order to evaluate players’ sprint performance for
different phases within the speed test (Brown et al. 2004). This will also allow
the tester to concurrently assess measures of acceleration, as described above.
Another method of evaluating maximal speed capabilities that is employed by
some in the field is to derive the maximum speed measure from the fastest
split time within the overall sprint. Commercially available electronic timing
gate systems are required, particularly if attempting to evaluate split times.
Testing agility performance
Commonly employed ‘agility tests’ in fact assess only change of direction
performance: ‘agility’ is defined in terms of change of direction or velocity in
response to a stimulus (Sheppard and Young 2006). This stipulates that there
must be some element of reaction and/or decision-making in any true
assessment of agility. Some change of direction tests do incorporate simple
reaction cues, such as responses to lights or similar. However, this does not
represent a valid measure of the game-related information-processing and
decision-making factors that contribute to team sports agility performance
(Sheppard and Young 2006).
Regardless of these issues, change of direction tests are of relevance: change
of direction abilities are a foundation of agility performance. As such, tests of
change of direction performance do provide important information, which
justifies their inclusion in any battery of tests for team sports players.
Tests of change of direction performance
A wide variety of tests that measure change of direction ability are employed
in different sports (Brughelli et al. 2008; Little and Williams 2005; Sheppard
and Young 2006; Young et al. 2001a). Protocols differ in terms of both
complexity and duration, and the statistical relationship between scores on
different change of direction measures varies accordingly (Sporis et al. 2010).
Two major considerations when selecting a test protocol are the extent to
which the protocol resembles the movement demands required in
competition, and also how much normative data exist for the test to provide a
reference against which to evaluate players’ scores. Factors such as whether
the protocol requires change of direction movements to be executed with the
dominant or non-dominant leg are also found to influence results (Meylan et
al. 2009). As with speed tests, these assessments are most reliable when
conducted with electronic timing gates.
The most basic change of direction tests comprise simple 180-degree turns.
For example, in the 5–0–5 test the player turns once to sprint 5m back to the
start line (Sheppard and Young 2006). The pro agility shuttle is a test that
features in the NFL Combine and is essentially an extended version of the 5–
0–5 test protocol (Sierer et al. 2008). The player sprints 5 yards, pivots 180degrees to sprint 10 yards in the opposite direction before executing a final
180-turn to sprint 5 yards back to the start line. The 9–6–3–6–9 test described
by Sporis et al. (2010) is run on a straight-line course that extends over a total
distance of 18m and comprises a total of five sprints of varying distances and
four 180-degree turns. The protocol consists of an initial sprint of 9m before
executing a 180-degree turn to sprint 3m in the opposite direction followed by
another 180-degree turn and sprint 6m in the original direction, then another
180-degree turn and 3m sprint before a final 180-degree turn and 9m sprint to
the finish line.
The ‘9–6–3–6–9 test with backwards and forwards running’ is a
modification to the above test which covers the same course, and involves
changing direction at the same points; however, the adaptation to the protocol
is that the test features only forwards and backwards running – so that the
athlete faces in the same direction (towards the finish line) throughout the
test. This version of the test was found to differentiate the particular change of
direction abilities of defenders and midfield players versus attackers in soccer
(Sporis et al. 2010). A number of shuttle change of direction tests also exist in
the literature that involve running a prescribed number of shuttle sprints over
varying distances. Examples include the 10 yard (9m) shuttle, 6 × 5m shuttle
and 4 × 5.8m shuttle tests (Brughelli et al. 2008).
Other change of direction assessments feature a combination of 90-degree
and 180-degree turns – one such example is the L-run test or the 3-cone drill
featured in the NFL Combine (Sierer et al. 2008) The course players run
features a cone placed 5 yards in front of the start/finish cone, with a third
cone placed 5 yards to the right of the second cone. The course thus features a
90-degree cut to the right, a 180-degree pivot and turn, and a 90-degree cut to
the left before the player returns to the start/finish cone. Of all the change of
direction tests employed in the NFL Combine, performance on the L-run test
was found to have the greatest correlation to draft pick ranking of American
football players selected for professional teams (Sierer et al. 2008).
The 4 × 5m sprint test described by Sporis and colleagues (2010) features a
set-up similar to the L-run test course, with the addition of another cone. The
protocol is identical to the one described above with an additional 90-degree
turn before a final 180-degree turn and 5m sprint to the finish line. The T-test
is a widely employed test of change of direction performance, which consists
of a 10m sprint forwards to a cone placed at the centre of the ‘T’, followed by
90-degree lateral cuts to reach cones placed 5m away to the left and right of
the centre cone before sprinting 10m back from the centre cone to the
start/finish cone. Different versions of this test also exist with modifications to
the distances between cones and the movement constraints imposed during
the test.
More complex and arguably more relevant change of direction protocols
consist of multiple cuts of varying degrees. For example, there are a variety of
zigzag run protocols, usually involving cutting change of direction movements
around three cones placed between the start and finish cones. The usual
cutting angle between successive cones is 100 degrees, and cones are typically
placed 5m apart (Mirkov et al. 2008). The Slalom test described by Sporis et al.
(2010) consists of a slalom course through six cones placed on a straight line at
2m intervals – the distance between the start line and the final cone is 11m so
the athlete covers a total distance of 22m. The athlete begins on the start line
with the first cone of the six-cone slalom course one metre away; the athlete
completes a slalom course through each cone in a forwards direction, then
performs a 180-degree turn after the final cone to complete the slalom course
in the opposite direction to finish back at the start line. The Illinois agility test
(Sheppard and Young 2006) is a well-established protocol that features
multiple slalom cuts through cones and 180-degree turns. Of all of the
standard change of direction tests the Illinois has possibly the greatest
complexity of movement, and the time required to complete the test is also
among the longest.
Change of direction tests that incorporate a sports skill component have
also been studied. For example, the reliability of a range of field-based tests of
change of direction, sprinting ability, and power for soccer players have been
investigated. Comparison of performance (that is, run time) on a change of
direction course when performed without a ball and whilst dribbling a ball
have also been used in order to provide a ‘skill index’ measure (Mirkov et al.
2008). While such tests may be useful for comparing scores of players within a
squad, a lack of adequate normative data for different populations makes
further interpretation difficult.
Assessments of ‘reactive agility’
Change of direction tests have been modified to incorporate a simple reaction
component to the movement task, so that the movement is executed in
response to an external cue. The time recorded by the athlete on tests of this
type therefore represents a combination of both reaction time and the time
taken to subsequently complete the movement task. Some commercially
available timing gate devices provide the facility for reactive tests, so that
when the athlete breaks a designated gate one of a selection of ‘finish’ gates
illuminates to indicate which direction the athlete must run to. Alternatively,
more simple field-based protocols involve the tester initiating the movement
response by performing a sidestep motion in the direction that the athlete is
required to move (Sheppard et al. 2006). More technologically advanced
protocols that have been employed in a research setting use a video display so
that the athlete is required to initiate the movement in response to movement
of players on the screen (Farrow et al. 2005).
Different reactive agility protocols have been investigated with various
groups of field team sports athletes. One study compared the same test
protocol, performed under both pre-planned conditions (the athlete was told
which gate to sprint to before the trial) and reactive conditions cued by a
video projection of a player passing the ball in the direction of the gate the
athlete was to sprint to (Farrow et al. 2005). Movement times are on average
slower in the reactive condition due to the perceptual component. However,
the difference between split times for pre-planned versus reactive conditions
were less for both highly skilled (national institute) and moderately skilled
(state-level) netball players, resulting in faster reactive agility times compared
to lesser skilled players (B-grade club players) (Farrow et al. 2005). As a result,
test measures recorded under reactive conditions also appear to be superior in
differentiating elite competitors from sub-elite players in these sports.
An investigation of the reactive agility test (RAT) protocol originally
described by Sheppard et al. (2006), which involves the athlete starting from a
stationary position and the movement response being triggered by movement
of the tester, reported similar results in Australian rules football players.
Players’ scores on the RAT protocol differentiated between players of different
playing standard, whereas a similar change of direction test under preplanned conditions was unable to do so. Very similar findings with respect to
superior reactive agility times as well as movement response accuracy have
also been reported for elite versus sub-elite rugby league players using the
same RAT protocol (Gabbett and Benton 2009).
Balance and stability testing
Single-leg balance and stabilisation
Static postural balance
Postural balance is defined as the ability of an individual to maintain their
centre of mass within their base of support (Hrysomallis 2007). Practically,
balance ability involves input from visual, vestibular, and somatosensory
systems (Hamilton et al. 2008). When assessing balance it is important
therefore to account for each of these subsystems that contribute to balance
ability. For example, an eyes-closed variation of a test removes visual system
input. Similarly, balance tests involving turning, or raising or lowering the
head, attempt to isolate vestibular system input.
Standard tests of balance ability commonly measure time that the player is
able to maintain equilibrium under a given set of conditions (for example,
stable/labile surface, eyes closed/open). Alternatively, the number of attempts
taken to balance under a given set of conditions for a specified time period is
recorded (Hrysomallis 2007). A field test of single-leg balance performed
standing with eyes closed for ten seconds was employed with collegiate
players competing in (men’s) American football, men’s and women’s soccer
and women’s volleyball (Trojian and McKeag 2006). Players’ scores on this
test were reportedly predictive of subsequent ankle injury incidence during
the playing season. Equipment such as ankle discs, foam mats and wobble
boards are also widely used for balance testing. Some balance board
apparatuses are built with contact sensors incorporated into the device in
order to detect loss of equilibrium, thereby providing a quantitative measure
when scoring the test (Hrysomallis 2007).
Force platforms (both laboratory-based and portable systems for field
testing) are commercially available that allow postural sway to be measured
by recording movement of the subject’s centre of pressure. Such equipment
can similarly be used to assess (static) postural control under given conditions
(bilateral/unilateral stance, eyes open/closed, etc.). Instrumented testing of this
type appears to be more sensitive in detecting deficits in postural control that
are predictive of injury risk (McKeon and Hertel 2008). In a research setting,
force plate centre of pressure and ground reaction force measurement has
been used in combination with tibial motor nerve stimulation, in order to
create ‘external’ disruption of balance and derive a ‘time to stabilisation’
measure (Brown and Mynark 2007). However, such testing involving costly
equipment and specialist staff to interpret the data is unlikely to be feasible for
routine testing of healthy players.
Dynamic postural balance
A popular field-based assessment of ‘dynamic’ postural balance is termed the
star excursion balance test (SEBT) (Bressel et al. 2007). This protocol requires
the athlete to balance on one leg while reaching out in various directions for
maximal distance with the opposite leg. The athlete is only permitted to touch
down lightly when marking their maximal reach distance in each direction –
the trial is discarded and repeated if they shift their weight onto the reaching
leg. The athlete is scored for distance reached in each direction and these
scores are corrected for limb length, in order to allow comparisons between
athletes (McKeon et al. 2008). Athletes’ scores on the SEBT were reported to
differ from their corresponding scores on a standard static balance test, which
led the authors of this study to conclude that this test assesses different
balance abilities (Bressel et al. 2007). This test also reports high sensitivity in
detecting deficits in sensorimotor function of the previously injured lower
limb in those who suffer from recurrent ankle injury (McKeon et al. 2008).
Preliminary data indicate that team sports players appear to exhibit superior
SEBT performance, based on comparisons between scores recorded by female
collegiate soccer players and healthy non-athlete female subjects (Thorpe and
Ebersole 2008). This would appear to support the contention that this test
evaluates relevant capacities for team sports players.
Tests of postural balance ability described above are commonly used as part
of screening prior to beginning a programme of physical preparation – see
section below. Scores on postural balance are frequently used to identify
players with chronic ankle instability (Brown and Mynark 2007). The other
common application is during rehabilitation – particularly following knee or
ankle injury – providing a tool to guide progression and to serve as a basis to
make judgements regarding readiness to return to full training or competitive
play (Wikstrom et al. 2006).
Dynamic stabilisation
Dynamic stabilisation can be defined as the athlete’s ability to maintain
equilibrium during movement (Brown and Mynark 2007). This capacity
comprises multiple aspects, including neuromuscular control and the
integrated function of various systems that provide dynamic stability to the
lower limb joints (Wikstrom et al. 2006). It has been identified that dynamic
stabilisation and static postural balance are discrete abilities, on the basis that
measures of the two abilities are not strongly related to each other (Brown
and Mynark 2007). Tests of dynamic stabilisation typically assess the player’s
ability to make the transition from movement to a stationary posture, for
example jumping or hopping onto either a stable or labile surface and holding
the landing.
Assessments of dynamic stabilisation in a laboratory or clinical setting
commonly involve hopping or landing from a box onto a force plate.
Measures recorded include postural sway, ground reaction force and time to
stabilisation (Wikstrom et al. 2006). Another assessment that has been used in
clinical and research settings uses electromyography (EMG). Surface EMG
electrodes are used to detect muscle recruitment and activity during
preparatory and reactive phases when subjects perform movement tasks or
respond to challenges in balance (Wikstrom et al. 2006). Such laboratory and
clinical assessments do, however, require specialised equipment and
appropriately trained personnel to interpret the test data. Given the cost, time
and access to specialised staff and equipment involved, these tests are
therefore likely to be impractical for routine testing for a squad of players.
Lumbopelvic ‘core’ stability
The particular combination of muscles that contribute to providing lumbar
spine stabilisation varies depending on posture and nature of the activity
(Juker et al. 1998). Furthermore, in a weight-bearing posture, the position in
which lumbopelvic stability is most commonly exhibited during sports
performance, the hip musculature that helps stabilise the pelvis and
supporting lower limb(s) also play a critical role. As such, during weightbearing, lumbopelvic stability has elements in common with postural balance
and dynamic stabilisation. There is therefore inevitably some cross-over into
postural balance and dynamic stabilisation when attempting to assess
lumbopelvic stability during upright stance or weight-bearing movements.
Given the complex and multidimensional nature of lumbopelvic stability
described, no standard test for core stability currently exists. Standard
endurance tests for the trunk muscles measure the time an athlete is able to
maintain a given position or posture (McGill 2007d). Examples of such tests
include the side bridge, flexor endurance test and static back extension
‘Biering-Sorensen’ endurance test (Carter et al. 2006). Normative data have
been published for these tests with healthy subjects as a reference for
comparison from the perspective of identifying low back injury risk (McGill
2007d). Ratios of flexor versus extensor scores and comparisons between sides
(in the case of side bridge) are suggested to be most useful in identifying low
back pain and injury risk. Data for these tests for athlete subjects have also
recently been published (Evans et al. 2007). In contrast to the data for nonathletes, the female and male athletes studied had comparable flexor and
extensor endurance times. However, side bridge endurance times were
significantly lower among the female athletes compared to male athletes
(Evans et al. 2007).
Another test more typically performed in a laboratory or clinic assesses the
player’s ability to maintain trunk muscle activation during challenged
breathing. The laboratory version of the test involves the player maintaining a
quarter squat position with weights held in the hands while breathing a
lowered oxygen and raised CO2 mixture – activity of core muscles is assessed
via EMG recordings (McGill 2007d). In a field-based clinical version of the
test, the player first performs a prior bout of exercise to raise their respiration
rate and the clinician then assesses their ability to maintain muscle activation
by palpating the player’s oblique abdominal muscles. The laboratory test
carries the usual issues of time, cost, equipment and need for specialist staff
common to all laboratory-based assessments – for this reason it is unlikely to
be included in a standard battery of tests for a large squad of players. The
field-based version of the test, while more practical and less costly, is
subjective and relies upon the judgement of a suitably trained clinician
(physiotherapist or athletic trainer).
Field-based clinical tests of torsional stability are becoming routinely
employed in functional screening protocols (see next section). Two examples
are the ‘push up test’ (of which there are two variations) and the ‘back bridge
test’ (McGill 2007d). The push up test is performed in an extended plank (push
up) position with the player alternately lifting off each supporting arm while
attempting to maintain a static posture (McGill 2006b). A variation of this test
involves alternately raising the supporting foot from the same extended plank
position. The back bridge is performed from a full bridge position (player is
supine supported on their heels and shoulders, knees flexed, hips raised off the
ground); while maintaining a stable position the player attempts to raise each
foot off the ground alternately (McGill 2007b). These tests are qualitative: they
are subjectively scored by the assessor upon set criteria (Cook 2003a).
Similarly, tests of torque generation involving projecting a medicine ball
from a seated posture have been used as a measure of the concentric ‘power’
of the core stabiliser muscles (Cowley and Swensen 2008). Variations of the
seated medicine ball throw in a sideways and backwards direction have also
been proposed (Shinkle et al. 2012). While preliminary data suggest that scores
on these tests may satisfy reliability criteria, the relationship with athletic
performance and/or injury risk remains to be established.
In much the same way as for postural balance, devices have also been
converted in order to measure ability to maintain equilibrium while holding a
core stability exercise posture. One study examined subjects’ core stability by
evaluating their attempts to maintain core stability postures on a stability
platform device commonly used to assess postural balance in standing
(Liemohn et al. 2005). There did appear to be a considerable learning effect
associated with this form of testing. Subjects were studied on four consecutive
days with the device: the data recorded on day three were found to be the
most reliable (Liemohn et al. 2005). Whilst this appears a promising area of
study, there is currently a paucity of published data with such testing
apparatus.
Musculoskeletal profiling and movement screening
Traditional musculoskeletal assessment protocols comprise static
measurements and clinical examinations of joint integrity and range of
motion, which mainly comprise passive assessment (Ford et al. 2003). There
are limitations to assessing neuromuscular and musculoskeletal factors in this
way: joints and muscles respond during passive tests in such a way that
limited information is provided on how the body behaves under dynamic
conditions. Another issue is that there is commonly inadequate follow-up to
screening: it has been reported that although musculoskeletal problems are
identified via such tests in 10 per cent of athletes, appropriate intervention is
typically undertaken in only 1–3 per cent (Ford et al. 2003).
That said, some clinical tests of musculoskeletal function have been shown
to be predictive of intrinsic (athlete-related) injury risk. Tests of joint range of
motion and muscle flexibility are recommended as a means to identify players
at risk of muscle strain injury. Pre-season baseline scores on quadriceps and
particularly hamstring flexibility were shown to be predictive of subsequent
muscle strains in Belgian professional soccer players during the following
playing season (Witvrouw et al. 2003). The authors concluded that scores
below 90 degrees on a passive test of hamstring muscle flexibility assessed in a
supine position identified players at risk of hamstring injury. A similar
relationship was reported with reduced ROM scores and adductor muscle
strains in a study of soccer players in Iceland (Arnason et al. 2004). Clinical
tests of joint integrity also typically identify joint laxity in the majority of
players who have suffered previous joint strains (Arnason et al. 2004).
Previous injury is often identified as a significant risk factor, so injury history
and such clinical tests of joint laxity are important to identify players at risk.
Although the application of isokinetic testing and training has been
questioned from a performance viewpoint, it does have applications for injury
prevention and monitoring rehabilitation. Isokinetic assessment of strength
ratios can help identify muscle strength imbalances that can predispose
players to injury; for example, comparisons of isokinetic internal and external
rotation strength measures for the shoulder have been used this way.
Comparison of isokinetic measures between previously injured and healthy
contralateral limbs appears to identify players at risk of recurrent hamstring
injury. These isokinetic scores and ratios (particularly eccentric and mixed
eccentric:concentric ratio measures) show potential for use as a test for
readiness to return to competition following a programme of rehabilitation
(Croisier et al. 2002). Similarly, isokinetic testing profiles assessing the optimal
angle (knee angle at the highest recorded concentric knee flexor torque) are
also shown to differentiate between injured limb and uninjured contralateral
limb in players with a history of recurrent hamstring injury (Brockett et al.
2004).
There are a number of dynamic tests of neuromuscular function and control
that are used in clinical settings for the purposes of screening for injury risk.
These are described in detail in Chapter 3. In addition, movement-based
screening protocols are seeing increasing use in the field, alongside or even in
place of standard clinical musculoskeletal assessments. These commonly
comprise active tests of mobility and stability, alongside qualitative
assessment of fundamental movement skill tasks – such as variations of squat
and lunge movements. The most commercially successful of these is the
Functional Movement Screen (FMS) devised by Gray Cook (Cook 2003a). The
use of these methods has become widespread in recent years, particularly in
the field of strength and conditioning.
Evaluating motor patterns and fundamental movement abilities is an area
of athletic assessment that is identified as having implications both for
performance and injury prevention (Cook 2003a). The rationale for this
approach is that players will tend to compensate for imbalances or areas of
poor mobility and reduced stability by adopting altered movement mechanics.
By their nature, these compensatory movement patterns are less efficient, and
are likely to inhibit performance and predispose the player to injury (Cook
2003a).
The rationale presented by Gray Cook for the FMS protocol and ‘functional’
assessment methods in general appears sound in theory, and anecdotally
many practitioners have used this form of assessment with some success.
Nevertheless, where possible each of the movement-based ‘screens’ selected in
a battery of assessments should have been validated in the literature.
Currently, there remains a lack of published data validating the FMS
assessment. One of the few investigations to date reported that individuals’
scores on the FMS showed only weak statistical relationships with selected
measures of athletic performance (Okada et al. 2011). Another study
investigated the relationship between FMS measures and a variety of standard
assessments of athletic performance (vertical jump, 20m sprint times and Ttest performance) and a sports skill task in collegiate athletes (golfers)
(Parchmen and McBride 2011). This study failed to find any significant
statistical relationships with any of the performance measures examined for
either the subjects’ combined FMS scores or their scores on the individual
FMS assessments. To conclude, there is currently insufficient evidence to
support the hypothesised relationship between FMS and athletic performance.
There also remains a need for studies to provide evidence in support of the
postulated link between the FMS assessment and incidence of injury.
There are examples in the literature of clinical tests designed to assess
functional performance that were not subsequently found to be predictive of
injury risk. Performance on a balance board test was found to have no relation
to ankle sprain injury incidence among high school athletes (McHugh et al.
2006). The rationale for assessing proprioception and postural stability in this
way would appear to be sound in theory from the point of view of injury
prevention, given that these are risk factors for ankle injury. However, the
lack of correlation found reinforces the fact that a causal relationship cannot
just be assumed and that tests must be validated to provide confidence in their
relevance. Given this, the inclusion of such tests in players’ musculoskeletal
screening and movement profiling would have to be considered until their
efficacy has been demonstrated.
3
NEUROMUSCULAR TRAINING
Introduction
Conceptually, neuromuscular training can be considered to comprise any
exercise mode that challenges a particular aspect of neuromuscular control
and co-ordination. As such, this type of training can take a variety of forms.
For example, neuromuscular training modes include strength training
exercises that impose various postural control and intermuscular coordination demands. Conversely, exercises that require balance and
stabilisation requiring postural and lower and/or upper limb control
performed without any external resistance – that is, body weight exercises –
comprise another form of neuromuscular training. In the latter case, exercises
of this type might also be performed on a stable surface, or alternatively may
incorporate a labile supporting surface or equipment such as stability balls or
other balance devices.
It is therefore evident that there are a large number and wide variety of
exercise modes that may be employed for neuromuscular training. Whatever
form it takes, the emphasis of neuromuscular training is on qualitative aspects
– such as the quality of movement. Accordingly, this type of training
necessitates a quite different approach to other forms of training. Specifically,
training parameters such as intensity, volume and frequency will be quite
different. With respect to intensity, rather than focusing on performing a
given movement against the highest resistance possible, progression of
training is achieved by manipulating the stability and mobility challenge
posed by the exercise. Similarly, volume for each session in terms of
repetitions and sets will be quite modest, as opposed to aiming to train to
fatigue. Conversely, the frequency of training is quite high, in order to
reinforce motor patterns and facilitate motor learning.
The necessity for neuromuscular training for athlete
populations
The fundamental movement capabilities of the athlete will help to determine
their proficiency in performing the specific movement skills required by the
sport (Gamble 2011c). The fundamental movements identified as being
common to most sports include variations of squatting and/or lifting
movements, pushing and/or pulling, lunging, gait (for example, running),
twisting movements and balance activities (McGill 2006c). In order to execute
these fundamental movements efficiently, the athlete must demonstrate the
requisite neuromuscular capabilities which underpin these movements. In this
way, different aspects of neuromuscular control and co-ordination ultimately
represent a limiting factor in the athlete’s abilities to execute the movements
of their sport effectively and efficiently. This relationship is depicted in Figure
3.1.
Figure 3.1 The role of neuromuscular function schematic
In addition to the general benefits of appropriate neuromuscular training
described with respect to enhancing the performance capabilities of the
athlete, certain populations have been identified as having a particular need
for corrective neuromuscular training. Specifically, young athletes (of both
sexes) and female athletes warrant particular attention and for both these
groups neuromuscular training should be considered a priority.
There is a strong interaction between motor skill development and the
processes of growth and maturation throughout the developmental years until
late adolescence–early adulthood (Naughton et al. 2000). The importance of
specific neuromuscular and movement skill training has therefore been
emphasised during critical phases before, during and after puberty (BarberWestin et al. 2005; Philippaerts et al. 2006). This is underlined by the reported
effectiveness of corrective neuromuscular training interventions with these
young athletes in reducing injuries sustained during youth sports (Emery and
Meeuwisse 2010).
Studies report improvements in strength scores and measures of lower limb
alignment in young males during the period spanning puberty and
adolescence (Schmitz et al. 2009) and this is reflected in an improved ability to
dissipate landing forces (Quatman et al. 2006). These naturally occurring
changes observed with young males during maturation are attributed to a
phenomenon known as the ‘neuromuscular spurt’, and are associated with
concomitant hormonal changes (Quatman et al. 2006). The continuing need
for neuromuscular training for young males should not be ignored, however,
as there are data to indicate that despite the neuromuscular spurt
phenomenon, some young males will still exhibit deficits in neuromuscular
control following puberty (Barber-Westin et al. 2006).
Female athletes do not benefit from the ‘neuromuscular spurt’
phenomenon: the same growth and maturation-related improvements in
strength and motor performance reported for males are not observed with
young female athletes. Studies report that deficits in measures of lower limb
control shown by female athletes are not corrected during growth and
maturation, and even appear to become more pronounced as these athletes
reach adolescence (Schmitz et al. 2009). As a result, significant differences in
neuromuscular performance are evident between males and females following
puberty that are not present among prepubescent boys and girls (Ford et al.
2010). For example, when compared to males, adolescent and adult female
athletes are shown to demonstrate different lower limb kinematics and
kinetics during drop-jump (Quatman et al. 2006) and stop-jump tasks
(Chappell et al. 2002), and sidestep cutting movements under both planned
(Hanson et al. 2008) and unanticipated conditions (Landry et al. 2007).
These gender differences in various indices of proximal control of the lower
limbs are identified as contributing to the increased incidence of lower limb
injury observed with female athletes (Mendiguchia et al. 2011). For example,
the injury surveillance data indicate that knee injuries are in the range of 2–10
times more prevalent in females (depending on the sport) compared to males
who compete in the same sport (Agel et al. 2005). This trend is apparent from
adolescence and continues into adulthood (Hewett et al. 2006b; Murphy et al.
2003). Again, the effectiveness of corrective neuromuscular training
interventions in reducing injury incidence among female athletes (Gilchrist et
al. 2008; Mandelbaum et al. 2005), and normalising reported rates of injury
towards the same range as those reported for male athletes (Hewett et al.
1999), points to the necessity of implementing preventative neuromuscular
training for all female athletes.
Dose–response relationship and
neuromuscular training effects
retention
of
Preliminary data indicate that neuromuscular training interventions show a
dose–response relationship. In particular, the frequency of training appears to
be a critical factor with respect to producing greater adaptations in
neuromuscular co-ordination (Carroll et al. 2001). For example, a study that
employed neuromuscular training intervention for injury prevention
identified a positive trend between the number of training sessions performed
and the degree of the protective effect observed in terms of reductions in
(non-contact) injury incidence (Kraemer and Knobloch 2009).
Similarly, the relative duration of a neuromuscular training intervention
appears to strongly influence the retention of neuromuscular training effects.
A recent study by Padua and colleagues (2012) assessed the retention of
positive changes to lower-limb control and mechanics resulting from a
neuromuscular training intervention with young team sports athletes (soccer
players). When assessed three months post-training, the group that had
performed the training for a nine-month period demonstrated better retention
of improved lower-limb mechanics and control compared to a group that had
performed the same training intervention for three months (Padua et al. 2012).
It is also apparent that compliance is critical in order to take advantage of
the beneficial effects of neuromuscular training (Soligard et al. 2010). While
this has been a major issue for some earlier studies, more recent studies that
have reported positive results often achieve good compliance by integrating
the neuromuscular training intervention into the players’ normal training,
such as during the warm-up (Kraemer and Knobloch 2009; Gilchrist et al.
2008). Education of coaches and players with regard to the necessity and
benefits of neuromuscular training interventions is also identified as a key
factor for achieving compliance (Soligard et al. 2010).
Identifying deficits in neuromuscular control
In much the same way as for other forms of training, testing serves an
important function when undertaking neuromuscular training interventions.
Appropriate assessment provides a means to initially evaluate the athlete, and
subsequently can serve as a tool to monitor the athlete and thereby guide
training progression. A variety of assessments exist in the literature that are
designed to assess a particular aspect of neuromuscular control and dynamic
function. These assessment modes essentially fall into two categories:
• Assessments of balance or ability to maintain equilibrium under a given set
of conditions;
• Tests that qualitatively evaluate lower limb alignment and mechanics
during movement-based tasks.
Assessing balance abilities
Balance involves a host of sensorimotor capacities, comprising input from
visual, vestibular and somatosensory systems (Bressel et al. 2007). Definitions
are important for clarity: discrete types of balance ability have been identified
and these are relatively independent of each other. Definitions of balance are
typically described with respect to a base of support, for example the ‘ability
to maintain centre of mass within base of support’. However, balanced
movement often comprises instances where the athlete is airborne. Examples
include the flight phase when running, which can comprise close to 75 per
cent of the gait cycle at maximal speeds (Yu et al. 2008), and also the flight
phase prior to landing movements. It would therefore appear necessary to
refine the global term ‘balance’, by describing this ability in terms of
maintaining equilibrium without specific reference to the base of support (if
any) involved.
Discrete abilities within the global term ‘balance’ have been identified in
the literature: static postural balance, dynamic postural balance, and dynamic
stabilisation; the distinctions between these abilities are detailed below.
Static balance Ability to maintain centre of mass over a static base of
support and stationary supporting surface (Bressel et al.
2007)
Dynamic
Capacity to maintain centre of mass over a fixed base of
balance
support under a movement challenge; specifically, motion
of other limbs and body segments, or unanticipated
disturbance to the supporting surface (DiStefano et al.
2009)
Dynamic
Ability to maintain equilibrium during the transition
stabilisation from motion to a stationary position, such as a landing
movement (Myer et al. 2006a)
Various forms of neuromuscular assessment also exist to evaluate each of
these different balance abilities. Essentially these balance testing modes assess
the athlete’s ability to retain their equilibrium under a given set of conditions.
This can be evaluated in a variety of ways, depending on the type of balance
ability assessed and the equipment employed during testing.
In an applied or clinical setting, static balance is typically assessed as the
number of attempts required to balance for a predetermined time duration
under a given set of conditions (eyes open/closed, head movements in various
directions), possibly alongside some subjective assessment, such as the degree
of effort and amount of corrective action the athlete displayed during the
assessment. Assessments of dynamic balance typically challenge the athlete to
reach the other limb(s) as far away from their base of support as possible
while retaining their balance – the most commonly used test is the star
excursion balance test (Bressel et al. 2007). Tests of dynamic stabilisation
typically involve jumping or hopping onto either a stable or labile surface;
upon landing the athlete attempts to maintain their equilibrium – that is,
‘stick’ the landing without taking a step or losing balance. To date, the use of
these tests has been largely restricted to a research setting, employing
specialised apparatus to quantify measures such as postural sway. In a field or
clinical setting more subjective assessment criteria will be need to be
implemented.
Movement-based assessments
function and control
of
neuromuscular
A number of assessment modes are employed to evaluate neuromuscular
function and dynamic control during closed kinetic chain movements from a
fixed base of support, as well as landing, pivoting and cutting movements.
These ‘neuromuscular assessment’ modes vary in terms of the level of
sophistication of the measurement and equipment employed, reflecting their
application in research versus applied settings. A number of simplified
versions of these assessment modes have been developed for use as a
screening and monitoring tool that can be conducted by those staff who work
closely with the athlete.
One such example is the single-leg squat, which is widely used in a clinical
setting to evaluate neuromuscular control and function of muscles of the hip
complex (Crossley et al. 2011). In particular, this test is designed to assess
proximal control of lower limb alignment – that is, positioning and movement
of pelvis, hip and knee in relation to the athlete’s supporting foot and torso.
The single-leg squat exercise is typically performed with body weight
resistance only; however, versions of this assessment mode performed with
external resistance also appear in the literature (Shields et al. 2005).
Preliminary data indicate that clinicians’ ratings of performance on this test
based upon specified criteria are indicative of measured differences in hip
muscle activation as well as differences in selected measures of hip and trunk
muscle function between subjects (Crossley et al. 2011).
Drop jump screening is another assessment method that has become a wellestablished tool in a clinical setting to evaluate neuromuscular function and
control under more dynamic conditions. In much the same way as the singleleg squat, this test is employed to assess proximal lower limb control during a
relatively basic movement-based task. In particular, this mode of testing
examines the athlete’s ability to maintain lower limb alignment during both
landing and take-off, and additionally the ability to resist knee abduction
moments of force during these movements. The drop jump test in its original
format as employed in a research setting has likewise recently been adapted
for use in a clinical and applied setting (Myer et al. 2010). This version of the
test requires only a digital camera and a standard laptop or desktop personal
computer. Furthermore, capturing the relevant images at landing and take-off
from the video recording and the subsequent analysis can be conducted using
software that is available free of charge via the internet.
Importantly, this clinical or field version of the drop jump test has reported
close agreement with laboratory-based measurements, which indicates that it
is a similarly valid tool for evaluating frontal plane lower limb alignment in
order to detect neuromuscular control deficits (Myer et al. 2010). Likewise,
assessments of this type do appear to be sufficiently sensitive to register
improvements in neuromuscular control elicited by neuromuscular training
interventions (Noyes et al. 2005). A limitation of this field or clinical version
of the drop-jump test is that as it only provides a picture of lower limb
alignment in a single plane of motion (frontal plane). One caveat therefore is
that it does not provide a true representation of neuromuscular control during
more complex multi-planar movements (Noyes et al. 2011).
There are various examples in the sports medicine literature of assessments
which evaluate neuromuscular function during more complex athletic
movements, such as pivoting and cutting change of direction movements. At
this stage the application of these assessments has been limited to a research
setting, and these laboratory-based protocols require specialised apparatus and
trained technicians to operate the equipment and analyse the data. However,
there is the potential for field-based versions of these tests to be developed and
validated to provide a clinical tool that is readily accessible to those who work
with the athlete. One such example is the bound and cut test that featured in a
recent study by Imwalle and colleagues (2009).
Neuromuscular training for postural control and
balance
Static balance training
In the case that the athlete’s screening has identified a deficiency in their
static balance abilities there is a clear need for dedicated training to improve
this capacity. In general it would also appear prudent to incorporate some
form of static balance activities in the day-to-day training of all athletes. Static
balance training is also likely to be beneficial for young athletes, particularly
at critical stages in their growth and development. Similarly, static balance
training is highly relevant to female athletes of all ages, given the prevalence
of lower limb injury and associated neuromuscular control issues observed in
this population.
Various constraints can be employed during static balance training tasks in
order to isolate or emphasise a particular component. For example, performing
the balance task with eyes closed eliminates visual input. Conversely, tilting
or turning the head modifies the challenge with respect to vestibular system
input. Finally, performing the balance task without shoes eliminates the
stabilisation provided by the athlete’s footwear, thereby accentuating
proprioceptive afferent input from cutaneous and joint mechanoreceptors. All
of these constraints may be manipulated individually or in combination in
order to progress the challenge posed by the balance task.
Dynamic balance training
There are essentially two approaches to developing dynamic postural control.
The first method is typically performed on a stable supporting surface and the
athlete is challenged to maintain equilibrium whilst performing
predetermined movements with the other limbs and body segments from a
fixed base of support. One example of this form of dynamic balance training
task is the star excursion balance test (Bressel et al. 2007). This is a single-leg
balance task that requires the athlete to reach out with the contralateral
(opposite) leg away from the supporting foot in a variety of directions, aiming
for maximum distance.
The alternative form of dynamic balance training involves balance tasks
performed on unstable supporting surfaces. This form of training employs
labile surfaces (for example, foam pads or inflatable cushions) or training
devices such as ‘wobble-boards’ or ‘tilt-boards’ (DiStefano et al. 2009). In
contrast to the former approach, this form of dynamic balance training
requires the athlete to minimise motion of limbs and body segments whilst
balancing on a movable base of support. Training adaptations following
dynamic balance training of this type appear to be mediated predominantly
by changes in central or ‘supraspinal’ neural input (Taube et al. 2007).
A variety of training regimens employing unstable training modes have
reported improvements in dynamic balance measures with athlete subjects
and some carry-over of these training effects to static balance abilities is also
evident (DiStefano et al. 2009). Progression can be achieved with the
particular dynamic balance training device by manipulating the same
constraints as described for static balance training. Examples of such
progressions include employing head movements, visual tracking tasks and/or
introducing an eyes-closed variation of the task.
Finally, the two forms of dynamic balance training can be combined by
employing exercises on an unstable surface that require the athlete to
maintain equilibrium whilst performing movements with the non-supporting
lower limb and/or upper limbs.
Dynamic stabilisation
Feed-forward control of ankle stabilisers during the preparatory phase prior to
touchdown is suggested to be the most important factor in improving active
stabilisation during landing or stopping movements (Holmes and Delahunt
2009). This is a learned effect and thus amenable to development via repeated
exposure to relevant movements in conjunction with appropriate coaching
(Zuur et al. 2010). A variety of landing tasks can be employed, depending
upon what is demanded by the characteristic athletic movements employed in
the sport.
Figure 3.2 Single-leg balance and head turn on domed device
Variations of these dynamic stabilisation training tasks can also be
performed landing onto an unstable surface by employing labile surfaces and
unstable training devices, as described for dynamic balance. Progression can
also be achieved by performing dynamic stabilisation tasks under reactive
conditions (McKeon et al. 2008). Qualitative criteria can be employed in order
to assess the quality of each attempt with dynamic stabilisation tasks.
Movement ‘errors’ include touching down with opposite (non-stance) leg, loss
of control in trunk posture or motion, and bracing non-stance limb against
supporting leg when attempting to balance following landing (McKeon et al.
2008).
‘Movement skills’ neuromuscular training
Corrective neuromuscular training interventions that are reported to be
successful in reducing incidence of injury often include some form of
movement skills instruction and practice (Hewett et al. 2006a). A good
example is the sportsmetrics training protocol developed at the Cincinnati
Sports Medicine Research and Education Foundation, which has been
documented to successfully reduce injury incidence among female athletes
predisposed to lower limb injury (Hewett et al. 1999). A key element of this
protocol is instruction and coaching of safe movement mechanics for common
athletic movements (for example, jumping and landing).
By happy coincidence ‘safe’ movement mechanics and postures are often
also more efficient and more effective. Adopting ‘safe’ movement mechanics
is frequently shown concurrently to improve performance, particularly when
the subjects in these studies exhibit suboptimal neuromuscular control or
movement patterns prior to the corrective training intervention.
For example, a neuromuscular training intervention for high school and
collegiate female basketball players achieved alterations in movement
mechanics during a stop jump movement that resulted in a 50 per cent
reduction in measured shear forces at the knee, and players’ jump height
performance was maintained or improved with the altered technique (Myers
and Hawkins 2010). A number of studies have reported improvements in
speed and change of direction performance alongside the changes in
movement mechanics elicited by this form of training with female athletes
(Hewett et al. 2006a).
Recently, modified versions of these generic corrective neuromuscular
training protocols have been developed which aim to deliver more
comprehensive instruction and development of the specific movement skills
that feature in a given sport. For example, a protocol has been developed for
high school volleyball players which incorporates locomotion and change of
direction movements, as well as a variety of jumping and bounding activities
(Noyes et al. 2011). Preliminary data indicate that this more progressive
approach to neuromuscular training confers greater improvements in athletic
performance (vertical jump) in comparison to those observed with more
established corrective neuromuscular training protocols. This protocol was
also similarly effective in eliciting significant improvements in measures of
neuromuscular control during a drop jump assessment (Noyes et al. 2011). The
latter finding is perhaps unsurprising as the training featured in this study
included the same exercises that feature in corrective neuromuscular training
protocols proven to improve neuromuscular indices and reduce injury
incidence, in addition to the novel exercise modes.
Figure 3.3 Compass bound and stabilise onto domed device
The application of neuromuscular training to improve athletic performance
is not a new concept. In track athletics the importance of ‘neural’ training has
long been emphasised, and this form of training is commonly applied,
particularly with sprinters. It would seem to follow that employing a more
progressive approach to neuromuscular training for the locomotion movement
skills that feature in other sports, such as team sports and racquet sports,
might confer performance benefits as well as addressing injury risk factors
(Gamble 2011c). In these more complex sports there is often an assumption
that athletes will naturally acquire the requisite athletic movement skill
development during the course of their technical and tactical development.
This notion may not be valid – anecdotally there are a number of examples in
these sports of athletes who have highly developed technical and tactical skills
but are lacking in athleticism and movement abilities.
Neuromuscular training in this form can therefore serve dual aims:
• Addressing known biomechanical injury risk factors;
• Enhancing movement efficiency and performance.
Assessing movement skill competencies
As has been described in an earlier section, there are tools available to
evaluate neuromuscular function during basic athletic movements, for
example single-leg squat and vertical drop jump landing and take-off
activities. These forms of assessment offer a valid means to identify gross
deficits in neuromuscular function and control. However, qualitative
assessment of movement skill competencies during more complex movements
is likely to require more subjective assessment using the trained eye of a coach
or practitioner. While speculative, it is likely that this type of qualitative
assessment is best conducted by observing the athlete in their natural training
and competition environment.
Unfortunately, the ability to recognise good versus poor athletic movement
is a skill that is rarely taught. Rather this tends to be a skill that comes from a
great deal of observation and experience. The ability of a coach or practitioner
to be able to correct and develop good movement skills by coaching
intervention is rarer still.
Neuromuscular training to develop locomotor abilities
Whilst established neuromuscular training protocols are often reported to be
effective in improving landing mechanics as well as favouring vertical jump
performance, it has been identified that there may be a lack of transfer to
more complex athletic activities with these protocols. For example, DiStefano
and colleagues (2011) reported that a standard corrective neuromuscular
training protocol failed to produce any improvement in lower limb kinetics
assessed during a reactive cut task in a group of prepubescent athletes. These
findings might be interpreted with a degree of caution given that studies
report that young athletes at this early stage of development appear to be less
responsive to neuromuscular training interventions. However, a more
progressive neuromuscular training protocol which featured cutting
movements under both preplanned and reactive conditions was successful in
producing some improvement in lower limb kinematics in the same subject
population (DiStefano et al. 2011).
It has been identified that ‘proximal’ neuromuscular control of the lower
limb demonstrated by athletes varies in a task-dependent manner
(Mendiguchia et al. 2011). It is therefore not entirely surprising that changes in
neuromuscular function and control developed during particular types of
activities (for example, straight-line hopping and bounding tasks) may not
carry over to other activities, particularly those which involve different planes
of movement. In view of the apparent specificity of neuromuscular training
effects, it follows that in order to develop neuromuscular function and control
for pivoting and other change of direction tasks (for example, cutting
movements) these specific movements must feature in the neuromuscular
training intervention.
Furthermore, lower limb neuromuscular control also differs for the same
task according to the conditions involved – specifically, whether the
movement is executed under pre-planned versus reactive or unanticipated
conditions (Besier et al. 2001). It therefore follows that not only must the
neuromuscular training protocol incorporate the relevant pivoting and change
of direction movements for the sport, but the constraints imposed during
training must also reflect the unplanned and reactive conditions encountered
during competition.
4
METABOLIC CONDITIONING
Introduction
The metabolic conditioning of a team sports player serves a crucial role in
defining and ultimately limiting their contribution to the game (Helgerud et
al. 2001). The effectiveness of players’ conditioning and resulting level of
fitness is a critical factor that determines their ability to fulfil the specific
demands imposed by the playing position.
Specificity in relation to metabolic conditioning involves both energy
systems and modes of activity. The bioenergetics of the training activity will
determine the impact of training on different aspects of metabolic
conditioning – such as aerobic versus anaerobic adaptations. In much the
same way, the benefits of metabolic conditioning are reflected principally in
the mode(s) of locomotion employed during training. Conditioning responses
show a high degree of training mode specificity (Jones and Carter 2000),
particularly in trained athletes (Millet et al. 2002a).
To satisfy training specificity, it follows that the format of conditioning for
team sports should employ the same modes of activity featured in the sport
and aim to impose corresponding stresses on metabolic systems to those
experienced during match-play. In accordance with this contention, sportspecific conditioning modes that replicate and overload physiological and
kinematic conditions encountered during athletic performance are identified
as being most effective for preparing players for competition (Deutsch et al.
1998).
Applying metabolic specificity thus essentially requires the format of
conditioning to reflect the parameters of competition. Practically achieving
this for a team sports player poses unique difficulties. Team sports rarely
involve continuous locomotion at a consistent intensity. Devising training to
exert proportionate stresses upon energy systems for the modes of activity
identified for a particular team sport therefore represents a considerable
challenge.
Metabolic conditioning and team sports performance
It is reported that measures of fitness for players in sports such as soccer are
significantly related to distance covered in a game (Castagna et al. 2010; Reilly
1994). Level of fitness also shows significant correlation to the number of
high-intensity efforts players attempt (Helgerud et al. 2001). Hence, metabolic
conditioning influences players’ work rate and also their involvement in the
game. The relationship between endurance fitness parameters and running
performance in matches (total distance covered and high-intensity running
bouts completed) are to some extent position-dependent in these team sports
(Buchheit et al. 2010c). This reflects the influence of playing position, and
other aspects of team strategy and tactics on patterns of activity during
matches and the associated endurance demands for players in team sports
such as soccer.
In general, a player’s ability to retain their capacity to perform highintensity efforts at the key moment is often crucial in the events that
ultimately decide matches (Drust et al. 1998; Reilly 1997). This can be via a
positive influence: making a break or evading a tackle, keeping up with play
to be available in support at the critical instant, or being able to chase back in
defence to make a crucial intervention. Likewise, it can be telling in a negative
sense – such as missing a tackle or interception, failing to support a teammate in possession of the ball leading to an attack breaking down, or being
unable to cover in defence at the critical moment.
Methodological challenges for profiling demands of
team sports competition
Attempts to quantify demands of team sports as a basis upon which to model
sport-specific conditioning practices have commonly analysed players’
movements during match-play. Distance covered during the course of a match
is often recorded as a global measure of energy expenditure and physiological
demand (Reilly 1994). Previously, time–motion analysis has been employed to
document the types of activity players engage in during a match (Duthie et al.
2003; McInnes et al. 1995). These methods were highly time-consuming. Over
recent years, the development of global positioning system (GPS) technology
and its increasing use in a professional team sports setting has provided a
much faster and easier means to quantify distance covered by players during
both competition and training (Aughey 2011). In addition to total distance,
this technology also allows distance covered per minute to be evaluated for
players wearing a GPS device.
However, intermittent sports have been shown to have energetic demands
far in excess of those that would be predicted from covering the same distance
continuously (Drust et al. 2000). It is notoriously difficult to evaluate
physiological stresses associated with intermittent sports by indirect methods,
such as time–motion analysis (Gamble 2004a; Reilly 1994, 1997). Similarly,
despite the technological advances of GPS, its reliability and validity for
quantifying high-intensity efforts is still questionable (Coutts and Duffield
2010). In general GPS devices with higher sampling rates provide more
accurate data; however, the greater the velocity of locomotion, the more error
is associated with GPS measurement. These factors are compounded by the
relatively brief durations of high-velocity bouts during matches, which further
decrease the likelihood of accurate measurement of distances for highintensity running bouts completed by players (Aughey 2011).
The intermittent nature of match-play activity in different team sports is
illustrated by studies such as that of McInnes and colleagues (1995), which
identified 997±183 movements during the course of a basketball match, with
transitions between modes of activity on average every 2 seconds. A study
examining rugby union football has similarly reported 560 discrete activities
during a 70-minute age-grade match (Deutsch et al. 1998). Bangsbo and
colleagues (1991) likewise recorded 1,197 changes in activity during a 90minute professional soccer match. Such intermittent and variable patterns of
exertion have major implications for the bioenergetics, and in turn the
conditioning demands, of team sports. The frequent changes in direction and
velocity of movement require inertia to be repeatedly overcome, and involve
accelerations and decelerations which constitute considerable added metabolic
and physiological demands (McInnes et al. 1995; Wilkins et al. 1991).
Without the facility to quantify the player’s inertia, and the associated
physiological costs of changes in velocity (that is, both speed and direction),
the GPS data in isolation will therefore fail to reflect the metabolic demands
associated with team sports play. Even when performing straight-line
running, the physiological costs of performing intermittent bouts under
controlled conditions on a treadmill is associated with greater physiological
strain (higher ratings of perceived exertion and ventilatory responses) than
exercise of the same average intensity performed continuously (Drust et al.
2000). Performing intermittent bouts of shuttle running with 180-degree turns
is similarly found to significantly increase physiological and metabolic
demands, in comparison to intermittent bouts of straight-line running
performed at the same speed for the same duration (Dellal et al. 2010). This
finding was apparent even in the elite senior team sports players studied,
despite their familiarity and skill performing these change of direction
movements. The added demands of changes in velocity when performing the
intermittent activity required during team sports play are likely to necessitate
a greater contribution from anaerobic metabolism, based upon the elevated
blood lactate concentrations observed (Dellal et al. 2010).
In addition, studies show that unorthodox (sideways and backwards) modes
of locomotion feature prominently in team sports, with certain playing
positions having a particular emphasis on these modes of locomotion (Duthie
et al. 2003; McInnes et al. 1995; Reilly 1994; Rienzi et al. 1999). The metabolic
demands of these movements are greater than conventional running in a
forwards direction (Reilly 1997), and this added physiological cost rises
disproportionately with increases in speed of movement (Reilly 1994). Gamerelated activities similarly impose considerably higher energy expenditure
than running (Reilly 1994, 1997). These factors further compound the
underestimation of physiological cost of match-play for team sports from
indirect observation such as time–motion analysis or GPS data.
Even when the metabolic cost of these unorthodox forms of locomotion and
game-related activities are quantified and taken into account, the transitions
between movements are of similar importance to the individual component
activities themselves. Estimations based on the individual component
activities performed in isolation will therefore underestimate the physiological
stresses imposed on players, and can thereby give a false indication of the
metabolic pathways implicated in real game situations.
Direct monitoring of physiological indices during matches
It follows that accurate assessment of exertion levels requires players to be
directly monitored during competition. The consensus is that assessment of
energetic demands in team sports should include sampling of markers of
physiological stress under performance conditions (Duthie et al. 2003;
McInnes et al. 1995; Reilly 1994; Reilly 1997). Despite technological advances,
gas analysis apparatus will inevitably restrict players’ movements and
interfere with match-play, and certainly would not be safe for contact sports.
In view of this, studies to assess energy expenditure typically use heart rate
(HR) or blood lactate (BLa) as the physiological marker (Reilly 1994).
The main argument against BLa as an index of exertion levels during
competitive matches is the dynamic nature of lactate as a metabolite (Bangsbo
et al. 1991). Blood lactate levels are essentially determined by relative rates of
production, release, uptake and removal. Consequently, single blood samples
merely give a snapshot of the activity performed during the interval
immediately prior to when the sample was taken. Concentrations of blood
lactate are commonly used to indicate contribution of anaerobic glycolysis to
energy production (Coutts et al. 2003). However, beyond establishing that
anaerobic metabolism plays a role in match-play exertion for a given sport,
sporadic determination of BLa is of little value in profiling activity or intensity
patterns throughout a match (Impellizzeri et al. 2005). Theoretically, serial
measurements of BLa may better reflect shifts in intensity of exertion
throughout a game, but the frequency of sampling required would be
unfeasible during a competitive match.
Assessments of the demands of competitive matches have thus tended to
favour HR monitoring as the sole reliable and practical indicator of
physiological strain or energy expenditure (Boyle et al. 1994). There is some
indication that the elevated HR values recorded under competitive conditions
will tend to overestimate the actual energy costs of match-play (Hill-Haas et
al. 2011). That said, the relationship between HR recorded and measured
oxygen uptake (VO2) during match-play activities (5-a-side games) is reported
to be robust and comparable to the HR–VO2 relationship assessed under
laboratory conditions (Castagna et al. 2004). Combining both HR monitoring
and analysis of accompanying GPS data has the potential to offer greater
insights into the demands of competition in team sports.
Quantifying physiological demands of match-play in
collision sports
The element of violent bodily contact with opposing players and the playing
surface has tended to preclude direct measurement of physiological responses
during game-play in collision sports (Duthie et al. 2003). A consequence of
this failure to objectively define the specific demands of match-play is that
training specificity has often been neglected in the design of conditioning
regimes for players at all levels in these collision sports in past years.
The development of lightweight and miniaturised GPS devices has made
this technology more amenable to implementation for contact sports (Aughey
2011). However, given the intermittent nature of activity during matches and
issues of quantifying high-intensity activity with GPS described, combined
with the non-running physical work undertaken by players in these sports,
direct monitoring of physiological parameters such as HR would still be
required to augment GPS data. Attempts that have been made to implement
HR monitoring during match-play in contact sports such as rugby union and
rugby league have typically been limited to youth and semi-professional
playing grades (Coutts et al. 2003; Deutsch et al. 1998). The relevance of these
data for senior players at elite level may, however, be questionable.
Sources of variability when evaluating demands of sports
performance
The strength and style of play of the opposition will inevitably influence the
nature, frequency, duration and density with respect to time of activities
players are required to perform (Duthie et al. 2003; Woolford and Angove
1991). These aspects will similarly be affected by the officiating styles and
environmental conditions (Duthie et al. 2003). The referee has a major bearing
on the format the game takes in terms of number of stoppages and duration of
phases of play, particularly in highly technical sports such as rugby union, ice
hockey and American football. Similarly, environmental conditions will
influence tactics and the errors committed by both sides, which will in turn
influence the pattern and mode of activity players will be engaged in. Thus,
there is significant variation not only within a match but also between
consecutive games (Duthie et al. 2003).
Notwithstanding the difficulties outlined in gathering data pertaining to the
global demands of match-play as they relate to a team, individual roles of
particular playing positions within a team are also quite diverse (Duthie et al.
2003). Precise roles of the respective playing positions therefore vary between
teams, depending on their particular structured game plan, and associated
demands imposed upon players in different positions. This is reflected in the
GPS data derived from matches in team sports such as soccer: total distance
covered during matches has been observed to differ significantly between
different playing positions (Buchheit et al. 2010b).
A significant volume of data would therefore appear to be required to
overcome the inherent variability within and between games to establish an
accurate assessment of demands during competition that are representative
for a particular team. This demand is multiplied several-fold if the aim is to
gather a complete picture of the associated demands for individual playing
positions within that team.
Physiological and neuromuscular bases of team sports
endurance
Based upon the available evidence, a number of different physiological and
neuromuscular factors have been identified as critical to meeting the specific
endurance demands of team sports competition. Characteristically, physical
exertion during team sports is of an intermittent nature, comprising sprints
and other modes of high-intensity activity. These bouts of intense activity are
interspersed with periods of variable duration engaged in lower intensity
locomotion, during which active recovery and removal of lactate can take
place (Hoff 2005). Metabolic demands thus alternate between energy provision
for bouts of high-intensity work, and replenishing energy sources and
restoring homeostasis during the intervals in between (Balsom et al. 1992).
A capacity termed ‘repeated sprint ability’ has therefore been identified as a
key determinant of team sports performance (Glaister 2005). Studies indicate
that a number of discrete elements are associated with this ability, as will be
discussed in the following sections.
Repeated sprint ability
As implied in the title, repeated sprint ability describes the capacity to
perform repeated bouts of high-intensity work with short (incomplete)
recovery periods between successive efforts. Superior performance on
measures of repeated sprint ability differentiates players at elite level from
those competing at a lower standard of competition in team sports such as
soccer (Impellizzeri et al. 2008). Studies also report strong statistical
relationships between tests of repeated sprint ability and the number of highintensity efforts and total distance recorded during matches in team sports
(Rampinini et al. 2007a). These observations would seem to underline the
importance of this capability for team sports players.
What constitutes good repeated sprint ability is the capacity to record high
average sprint performance over successive sprint efforts. This requires the
player to be (a) fast, in order to record good sprint times for individual bouts,
and (b) able to maintain a high level of sprint performance during each
successive bout (Bishop et al. 2011). Repeated sprint ability is therefore related
to neuromuscular aspects associated with speed performance, as well as
physiological and metabolic components (Pyne et al. 2008). Combating the
effects of fatigue in order to maintain performance across successive efforts
similarly involves a variety of metabolic, physiological and neuromuscular
aspects (Girard et al. 2011a).
Anaerobic capacity
Anaerobic capacity represents an athlete’s endurance when performing an
exhaustive bout of running at supramaximal velocities (that is, above
vVO2max or MAS). This parameter is typically quantified via measures of
performance during maximal efforts over longer distances, for example
shuttle sprints over 300m (Moore and Murphy 2003), or average work output
relative to body mass during a 30-second all-out work bout, such as the
Wingate test (Zupan et al. 2009).
Anaerobic capacity is dependent upon factors such as the player’s muscle
fibre profile (type II fibres have higher anaerobic capacity), muscle glycolytic
enzyme content and activity, and lactate handling and muscle buffering
capacities (Maughan and Gleeson 2004). Despite the apparent relevance of this
aspect of conditioning with respect to intermittent exercise performance, it
has been highlighted that there is a lack of data pertaining to anaerobic
capacity of team sports players, especially those competing at elite level
(Duthie et al. 2003).
The content and activity of enzymes associated with glycolytic metabolism
are responsive to training (Kubukeli et al. 2002). However, as alluded to above,
the ability to mobilise glycolytic metabolism during repeated sprint bouts is
dependent on not only enzyme content but also the ability to offset the
inhibition of glycolytic metabolism due to the accumulation of metabolites.
Therefore lactate handling and muscle buffering capacity are similarly critical
factors.
Muscle buffering capacity
Athletes with a history of repeated sprint training are shown to exhibit an
enhanced ability to buffer the hydrogen ion accumulation associated with
glycolytic metabolism in order to minimise changes in muscle pH (Edge et al.
2006a). Buffering of hydrogen ions is important to counteract the inhibition
effects of acidosis and corresponding impairments in repeated sprint
performance (Bishop et al. 2011). The specific peripheral adaptations observed
with improvements in buffering capacity include increased capilliarisation of
muscle fibres (Jones and Carter 2000) and improved capacity of buffering
agents and up-regulation of lactate/H+ transporters within the muscle cell
(Billat et al. 2003). Similarly, appropriate conditioning can improve the
capacity for handling and clearance of metabolites from adenosine
triphosphate (ATP) breakdown, in particular inorganic phosphate (Pi) which
contributes to fatigue when performing repeated sprint activity (Glaister
2005).
Another relevant adaptation concerns the expression and activity of
sodium/potassium pumps within the muscle cell. Loss of potassium (K+) ions
from the muscle cell with repeated muscle activation during high-intensity
running exercise is identified as a key fatigue mechanism (Iaia and Bangsbo
2010). The action of sodium/potassium pumps works to counteract this loss of
K+ ions.
Lactate handling and metabolism
Oxidative processes within the muscle cell play an important role in handling
lactate produced via glycolytic metabolism. Lactate is used directly as a
substrate for oxidative metabolism within the mitochondria, and lactate is also
the main precursor for gluconeogenesis during prolonged exercise, a process
that produces glucose for carbohydrate metabolism (Brooks 2009). As this
capacity is exceeded during high-intensity exercise, lactate transporters within
skeletal muscle also act to remove excess lactate from the muscle cell during
exercise, in order to offset the inhibition of glycolysis. In particular,
monocarboxylate transporters (MCTs) in the muscle cell membrane are
identified as critical to the removal of lactate and H+ ions, and there is some
evidence that the expression of MCTs is responsive to appropriate training
(Bishop et al. 2011).
There is a large amount of evidence that lactate transported out of the
muscle cell can be taken up and metabolised by adjacent muscle fibres as well
as other organs, which serves to assist lactate handling (Brooks 2009). This is
the central tenet of ‘lactate shuttle’ theory. It is now well established that a
variety of tissues and organs use lactate as a substrate for energy metabolism
under both aerobic and anaerobic conditions, and that the contribution of
lactate to energy production can be considerable (Brooks 2009). In much the
same way as lactate produced via glycolytic metabolism is taken up by the
mitochondria within the muscle cell and used for oxidative metabolism,
lactate transported out of the muscle cell during high-intensity exercise can be
taken up and oxidised by adjacent muscle fibres within the working muscle –
particularly those with high mitochondrial capacity (Brooks 2009).
Aerobic capacity
Some authors have inferred that aerobic fitness is of lesser relative importance
based upon the comparatively lower values of VO2max reported for players in
some team sports, particularly in rugby union football and basketball (Duthie
et al. 2003; Hoffman et al. 1999). Measures of aerobic capacity have, however,
been reported to show significant statistical relationships with repeated sprint
ability (Bishop et al. 2004). Of the respective measures of aerobic capacity, it
has been suggested that vVO2max or MAS is of more relevance to repeated
sprint ability than VO2max or VO2peak, which may explain the modest
correlation between VO2max and repeated sprint ability scores reported in
some studies (Girard et al. 2011a).
Previously it had been suggested that the role of aerobic metabolism during
team sports play is limited to rest periods during stoppages between periods of
activity (Duthie et al. 2003). However, repeated sprint exercise of the type
featured during matches in fact involves a significant aerobic contribution to
energy production (Bogdanis et al. 1996a). Oxidative metabolism contributes a
major portion of the energy during successive efforts following the first sprint.
A study investigating repeated maximal 30-second bouts reported that the
aerobic contribution increased from 31 per cent in the first 30-second sprint in
a set to almost 50 per cent in the second, even with four minutes’ recovery
between sprints (Bogdanis et al. 1996a). This increasing contribution from
aerobic metabolism serves to offset losses in power output resulting from
reduced capacity for anaerobic energy production. More recent investigations
reported that peak VO2 values recorded during successive 30-second all-out
efforts are observed to reach close to VO2max even in trained athletes
(Buchheit et al. 2012; Girard et al. 2011a).
Aside from the direct contribution of oxidative metabolism to energy
production during successive sprint efforts, the role of aerobic capacity during
rest intervals is another key aspect. Oxygen uptake kinetics measured during
recovery periods are identified as a key component of repeated sprint ability
(Dupont et al. 2010). This is indicative of the relationship between the
oxidative capacity of muscle and the oxygen-dependent processes associated
with phosphocreatine (PCr) resynthesis during the recovery intervals between
work bouts (Bogdanis et al. 1996a). It is identified that PCr is a particularly
important high-rate energy source for repeated sprint exercise, and marked
depletion of muscle PCr stores (35–55 per cent) is observed following a 6-
second sprint bout (Girard et al. 2011a). Rest intervals between high-intensity
efforts in team sports are typically too brief to allow for complete restoration
of PCr stores (Spencer et al. 2005), which can take in excess of four minutes
(Bogdanis et al. 1996a); therefore, improving the initial fast component of PCr
resynthesis is key to supporting repeated sprint ability.
It appears that peripheral components of aerobic capacity, as opposed to
cardiopulmonary aspects, are most influential with regards to repeated sprint
ability (Bishop et al. 2004). Muscle oxidative capacity and peripheral
adaptations resulting in improved muscle reoxygenation during rest intervals
are suggested to be most relevant when performing repeated sprint activity
(Girard et al. 2011a). An investigation of physiological responses during a
maximal intensity interval protocol (30-second all-out cycling bouts
interspersed with two minutes’ recovery) observed an increasing level of
deoxygenation at the muscle fibre during successive efforts, which is offset by
corresponding increases in rates of muscle reoxygenation during the rest
intervals between each work bout (Buchheit et al. 2012). A highly significant
finding is that improvements in repeated sprint ability following highintensity interval training are also found to be related to increases in muscle
reoxygenation rates measured during rest intervals (Buchheit and Ufland
2011).
Another potential adaptation associated with training to develop aerobic
capacity is an improved ability to utilise fat stores within the muscle as an
energy source during games, which will help to spare players’ finite glycogen
stores (Hoff 2005). This is significant adaptation in team sports such as soccer
where glycogen depletion during the second half of matches results in
decreased work capacity, reflected in decreased distances covered and reduced
high-intensity activity (Hoff 2005).
Maximum speed capabilities
When undertaking repeated sprint exercise the athlete’s sprint performance in
the first sprint bout shows strong statistical relationships with both their
performance in the final sprint bout, and their overall sprint performance
(Girard et al. 2011a). A player’s maximum speed per se is therefore strongly
related to their repeated sprint ability. In addition to genetically determined
anthropometric factors (such as limb length) and muscle fibre profile
(proportion of type II fibres), sprinting speed capabilities also involve a variety
of strength qualities and neuromuscular attributes, as discussed in Chapter 8.
Running economy and neuromuscular factors
Exercise economy is identified as a key component of cardiorespiratory fitness
(Jones and Carter 2000). Movement efficiency and economy during different
forms of locomotion are therefore key determinants of endurance during
matches. From this point of view, neuromuscular control and motor patterns
featured in training would appear to be a critical factor in terms of the carryover of metabolic conditioning to performance. In support of this, it has been
reported that measures of running economy when performing shuttle runs
showed a positive statistical relationship with weekly training and
competition volume in the team sports players studied (Buchheit et al. 2011b).
This would appear to indicate that exposure to training and matches which
feature game-specific movement patterns and change of direction activities
serves to enhance economy when performing these forms of locomotion.
Relevant neuromuscular adaptations that underpin running economy
concern intramuscular and intermuscular co-ordination (Girard et al. 2011a);
the ability to maintain these capabilities under fatigue is similarly a trainable
quality (Behm 2005). Repeated sprint running is associated with significant
reductions in force and power output of lower limb muscles during maximal
voluntary contractions and evoked muscle twitch responses, indicative of
peripheral fatigue (Perrey et al. 2010). Developing neuromuscular capabilities
and fatigue resistance may therefore help to reduce the decline in power
output and speed during successive sprint efforts.
Intramuscular co-ordination also comprises stiffness regulation of the
muscle–tendon complex of locomotor muscles. Alterations in lower limb
stiffness and spring properties have been observed during the course of a
repeated sprint protocol, which are reflected in progressive reductions in
sprint performance (Girard et al. 2011b). Another study reported that team
sports athletes demonstrated a superior ability to maintain stiffness regulation
during successive sprint efforts, which appears to reflect their training history
with this form of repeated sprint exercise (Clark 2009).
Factors determining relevant training adaptations
The nature of the conditioning response is dependent upon the work intensity
and volume and/or duration of training performed. Some changes, such as
growth in the size and capacity of the heart and increases in lung vital
capacity, are only apparent in athletes who have completed high volumes of
endurance training over a period of years. Other training adaptations are
much more responsive to training.
Enzyme adaptation
Increases in content and activity of anaerobic enzymes, specifically those
involved in glycogenolysis and glycolysis, have been reported with sprint
training (Kubukeli et al. 2002). It appears that relatively longer work bouts,
which require a greater contribution from glycolytic metabolism, are most
effective for eliciting increases in these enzymes, in comparison to repeated
sprint exercise involving shorter (≤ 10-second) work bouts (Bishop et al. 2011).
Conversely, relatively longer rest intervals appear to be beneficial from the
point of view of allowing a more complete return to homeostasis, in order to
limit the inhibition of glycolysis during successive work bouts. On that basis,
the optimal conditioning format for eliciting changes in glycolytic enzymes
would feature 30-second all-out work bouts, interspersed with extended rest
periods (>4 minutes) (Bishop et al. 2011).
A range of high-intensity interval training protocols involving work
intensities at or above vVO2max have reported improvements in enzymes
involved in oxidative metabolism. For example, ‘30-second sprint interval
training’ protocols involving repeated 30-second all-out efforts, that is, supra(VO2) maximal intensity, with rest periods of 4 minutes have consistently
shown these changes (Gibala and McGee 2008). This reflects the contribution
of aerobic metabolism during successive work bouts with this conditioning
format (Bogdanis et al. 1996). High-intensity aerobic interval training
involving longer (4-minute) work bouts conducted at close to vVO2max or
MAS intensity interspersed with 2-minute rest periods are also effective in
producing changes in oxidative enzymes (Talanian et al. 2007). With these
long aerobic interval methods it is recommended that the rest intervals
employed should be less than the duration of work bouts in order to maximise
the aerobic contribution and resulting adaptations in oxidative enzymes
(Bishop et al. 2011).
Energy substrate availability and restoration
High-intensity interval conditioning appears to be a potent training stimulus
for eliciting adaptations in muscle oxidative capacity (Gibala and McGee
2008), which supports the oxygen-dependent resynthesis of muscle PCr stores
during rest intervals between maximal efforts. Accordingly, preliminary data
suggest that high-intensity interval conditioning conducted at VO2max
intensity can elicit significant improvements in the initial rate (that is, the
‘fast component’) of PCr resythensis observed within the first 60 seconds
following high-intensity work bouts (Bishop et al. 2011). Adaptations
associated with high-intensity interval conditioning and repeated sprint
training that serve to reduce the breakdown and diffusion of substrates for
ATP resynthesis are also of relevance to repeated sprint ability (Glaister 2005;
Spencer et al. 2004).
Increases in resting muscle glycogen content have also been reported with
high-intensity training studies involving short-term 30-second all-out
intervals separated by 4-minute recovery periods (Gibala and McGee 2008).
There are some data to suggest that aerobic interval training promotes
oxidative metabolism of fats, in comparison to the same exercise performed as
a continuous bout (Billat 2001a). Relatively longer work bouts (≈4 minutes) at
correspondingly lower relative intensity (≈90 per cent vVO2max) appear to
promote these adaptations (Gibala and McGee 2008). The preferential use of
fats as an energy substrate and sparing of finite stores of glycogen
(carbohydrate) is an important adaptation in terms of prolonging the player’s
ability to perform at higher work intensities, given the significant depletion in
muscle glycogen that is observed towards the end of matches in team sports
such as soccer (Hoff 2005).
Capacity to clear and buffer metabolites
Training at moderate exercise intensity does not produce changes in lactate
clearance and muscle buffering capabilities (Tabata et al. 1996, 1997). A more
recent study reported that when matched for volume, short-term training (5
weeks) at an intensity just above lactate threshold elicits superior
improvements in buffering capacity than training at an intensity just below
the athletes’ measured lactate threshold (Edge et al. 2006a). The efficacy of
conditioning in developing anaerobic capacity is therefore intensitydependent, requiring training at intensities that exceed lactate threshold or
‘maximum lactate steady state’ intensity. By definition, the conditioning
stimulus must elevate lactate above steady state levels in order to stimulate
lactate handling and buffering mechanisms (Billat 2001b).
However, recent data indicate that the intensity of work bouts and relative
duration of work:rest selected should not elevate H+ concentrations
excessively so that muscle pH falls too far, in order to ensure a favourable
adaptive response, in terms of MCT isoform expression (lactate and H+
transport proteins) and intracellular buffering capacity (Bishop et al. 2008).
The training history of the athlete and buffering capacities at the start of the
training period may be an important factor in terms of what constitutes
appropriate training. Conversely, if rest periods between sets are too long and
thereby allow lactate and H+ concentrations to return towards baseline levels,
then this is also likely to limit the training stimulus for adaptations associated
with buffering capacity (Bishop et al. 2011). A range of repeated sprint and
high-intensity interval training protocols have reported positive changes in
buffering capacity and expression of MCT isoforms in various study
populations.
Peripheral adaptations supporting muscle oxygenation
Muscle oxygenation is dependent upon muscle blood flow (and therefore
oxygen delivery), and oxygen uptake and consumption at the muscle cell
(Buchheit et al. 2012). Relevant adaptations therefore include muscle
capilliarisation and muscle oxidative capacity (content and capacity of
mitochondria, and mitochondrial enzyme activity). Improvements in muscle
reoxygenation rates have been observed following a high-intensity aerobic
interval training intervention conducted at intensities in the range 90–115 per
cent MAS that also reported concurrent improvements in aerobic capacity and
repeated sprint ability (Buchheit and Uffland 2011).
Aerobic capacity and maximum aerobic speed
For well-trained athletes it is suggested that training intensities at or above
vVO2max or MAS are likely to be required in order to produce any further
improvements in aerobic capacity (Laursen and Jenkins 2002; Midgley et al.
2006). High-intensity and low-volume training interventions have been shown
to produce comparable improvements in endurance performance (over both
short and long distances) and similar changes in measured muscle oxidative
capacity in comparison to traditional moderate-intensity high-volume training
(Gibala et al. 2006). The similar improvements elicited by the high-intensity
conditioning group in these studies are particularly notable given both total
training time and volume with this approach is only a fraction of that
completed by subjects who performed moderate-intensity high-volume
training. It is suggested that part of this potency of high-intensity
conditioning is due to its recruitment of a larger pool of motor units during
the conditioning activity, and the greater use of larger high-threshold type II
muscle fibres, compared to submaximal conditioning protocols (Gibala and
McGee 2008).
Improvements in measures of aerobic capacity, including muscle oxidative
capacity and measures of vVO2max or MAS, have been recorded with a range
of high-intensity training formats. In some studies these improvements have
been seen without any measured changes in subjects’ VO2max scores (Gibala
and McGee 2008). The standard high-intensity conditioning protocol
employed in a number of studies consisted of four to six sets of 30-second allout efforts with 4 minutes’ recovery between sets. However, improvements in
aerobic capacity have also been produced with other high-intensity aerobic
interval training formats, including a protocol involving long aerobic intervals
involving 4-minute work bouts at close to vVO2max (Talanian et al. 2007,
2010). Similarly, a mixed protocol comprising both short (20–50-second runs)
and long (2:30–15-minute) intervals at a range of intensities (85–120 per cent
vVO2max) has also elicited improvements in measures of aerobic capacity,
including MAS scores (Buchheit and Ufland 2011).
Neuromuscular adaptations
Unsurprisingly, neuromuscular training responses relating to work economy
and movement efficiency are dependent upon the exercise mode used in
conditioning (Jones and Carter 2000). For example, the endurance
performance of elite triathletes on a given competition element (running,
cycling, or swimming) shows no relationship to the training completed by
these athletes on other elements (Millet et al. 2002a). In trained non-athletes,
cross training (swimming) is similarly shown to be inferior to running
training in improving running performance parameters (Foster et al. 1997).
Specificity of neuromuscular adaptations associated with running economy is
also apparent for running locomotion. For example, the amount of exposure of
team sports athletes to shuttle sprints and change of direction movements
during training and competition is related to their running economy measured
using a shuttle sprint protocol (Buchheit et al. 2011b).
It follows that it is necessary to replicate the type of locomotion and
movements encountered during competition when undertaking metabolic
conditioning in order to develop economy or efficiency. As such, conditioning
modes for team sports should necessarily include the change of direction
movements and unorthodox forms of locomotion (sideways, backwards and
tracking movements) that feature in matches (Reilly 1994).
Improvements in work economy are also specific to the velocity at which
conditioning is performed. For example, in runners the improvements
observed in running economy are greatest at the running velocity at which
the athlete habitually trains (Jones and Carter 2000). From this it appears that
conditioning performed should reflect the movement velocities encountered
during match-play in order to develop work economy at these specific
velocities.
By extension, improving repeated sprint ability by developing players’
maximum speed capabilities will require that their training includes
acceleration and sprint bouts performed at maximal velocity (Bishop et al.
2011). When different forms of training are employed in isolation, performing
sprinting-based training itself is shown to be the single most effective means
to improve sprinting-specific neuromuscular co-ordination aspects and
thereby sprint performance (Kristensen et al. 2006). In accordance with this, a
short-term training intervention solely comprising speed and acceleration
drills reportedly produced improvements in both acceleration and scores on a
test of repeated sprint ability in well-trained team sports players (Buchheit et
al. 2010b). In this study, equivalent improvements were not seen in another
group of players who completed high-intensity running conditioning
comprising 30-second shuttle sprint bouts with 2-minute recovery and
improved only in a measure of vVO2max or MAS at the end of the study
period.
Strength training also represents means to elicit neuromuscular adaptations
in order to improve movement efficiency and endurance performance.
Maximal strength training has proved to be effective in reducing oxygen cost
at a given workload with endurance athletes (Hoff 2005). It follows that
strength training similarly has a role to play for developing running economy
for team sports players. Improvements in measures of repeated sprint ability
have also been reported with an explosive strength training intervention with
young elite soccer players (Buchheit 2010). Exercise selection and the workout
format employed are likely to be decisive factors in determining the transfer
of strength training to work economy and repeated sprint ability for the
particular movements required during a match in a given team sport. The
potential for strength training to impact upon endurance performance is
discussed in greater detail in Chapter 5.
Training strategies to develop different aspects of
metabolic conditioning
High-intensity training methods
It is suggested that well-trained endurance athletes require higher training
intensities to produce further gains in performance and enhancement in
VO2max (Midgley et al. 2006). The requisite levels of intensity identified are in
the range of 95–100 per cent of the velocity attained at VO2max. By definition,
continuous work over an extended period is limited to submaximal work
intensities – higher work rates cannot be sustained over these longer periods.
Interval conditioning provides a framework to allow higher work intensities
to be performed over repeated bouts; this means that the accumulated total
time spent at these higher intensities is longer than would be possible if
working continuously (Billat 2001a).
By their intermittent nature, team sports would appear to be most amenable
to aerobic and anaerobic interval conditioning. Importantly, interval-based
conditioning also enables both aerobic and anaerobic capacity to be developed
simultaneously (Laursen and Jenkins 2002). This not only represents the more
‘sport-specific’ approach, but is also more time-efficient – this is an important
consideration in view of the volume of technical and tactical practices and
other training athletes in these sports are required to perform.
High-intensity interval training is shown to improve cardiorespiratory
fitness parameters and measures of performance in team sports athletes
(Helgerud et al. 2001). A range of conditioning modes have been used
successfully, including hill running (Helgerud et al. 2001) and high-intensity
game-related drills (McMillan et al. 2005). One such study reported increases
in aerobic power, lactate threshold and running economy observed in junior
elite soccer players following training that were also reflected in concurrent
improvements in performance measures. Significant increases were observed
in distance covered in a match, average work intensity in both halves of play,
number of sprints and frequency of involvement in play (Helgerud et al. 2001).
High-intensity interval exercise is shown to elicit significant concurrent
improvements in both aerobic power (VO2max) and a selection of anaerobic
capacity and intermittent exercise performance measures (Gaiga and
Docherty 1995; Tabata et al. 1996). If work bouts are conducted at paces that
correspond to those occurring during competition, this form of training will
also favour improvements in running economy and work efficiency at
competition velocities (Jones and Carter 2000).
High-intensity interval running conditioning
Investigations of interval training protocols have found aerobic and anaerobic
systems are taxed to a different relative extent depending on the format of
training: key factors are the intensity of work bouts and the relative length of
work and recovery phases (Tabata et al. 1997). For example, what separates
aerobic interval training from anaerobic interval training is the intensity and
relative duration of work and rest periods, so that either aerobic metabolism
or anaerobic metabolism predominates (Billat 2001a). It appears that optimal
combinations of high-intensity work bouts and brief rest intervals might also
exist that simultaneously tax both aerobic and anaerobic systems almost
maximally (Tabata et al. 1996, 1997).
Running intervals at individualised maximum aerobic speed
intensities
The emergence of a field test that allows an equivalent parameter to vVO2max
or MAS to be accurately evaluated for each player has facilitated the
development of a high-intensity interval running conditioning approach
involving work bouts conducted at individualised running speeds. Each player
is required to cover an individualised distance, determined by their MAS score
and the specified duration of each work bout. Practically, this is often
achieved using running lanes of varying length so that players run together,
and the respective distances covered are determined by the player’s individual
MAS score (and the duration of work bouts employed). The most common
work:rest formats featured in the literature are:
• 30 seconds’ work : 15 seconds’ rest;
• 15 seconds’ work : 15 seconds’ rest.
A modification to this approach can also allow anaerobic interval training to
be performed, by employing velocities above players’ measured MAS to
provide ‘supra-maximal’ work intervals. For example, a protocol involving 15second work bouts at 120 per cent MAS interspersed with 15-second rest
intervals has been described for soccer players (Dupont et al. 2004). In this
study, players recorded significant improvements for both aerobic capacity
(vVO2max) and 40m sprint times when this form of training was performed
twice per week during the playing season. Based upon physiological responses
observed with different work:rest combinations, it appears that supramaximal
work intervals (that is, >100 per cent MAS) may in fact be required when
shorter 10- or 15-second work bouts are employed in order to elicit the
requisite intensity for trained elite players (Dellal et al. 2008).
As described in the previous sections, an alternative approach is to perform
‘long’ aerobic intervals comprising work bouts typically ranging from 90
seconds to 4 minutes, performed at intensities close to vVO2max or MAS
(Billat 2001a). It is suggested with this approach that the rest bouts should be
relatively shorter than the work bouts, in order to maximise the aerobic
training stimulus (Bishop et al. 2011). For example, a high-intensity aerobic
interval training format that has proven to be successful involves repeated 4minute bouts performed at ≈90 per cent VO2max intensity, interspersed with
2-minute rest periods (Talanian et al. 2007, 2010).
This approach is highly structured and is beneficial in terms of delivery and
the ease with which individual players’ work rates can be monitored. This is
reflected in highly reproducible physiological responses when players perform
high-intensity interval running at individualised MAS intensities (Dellal et al.
2008). As a result, it is relatively easy to ensure consistent levels of work
intensity between sets and sessions.
On the other hand, the exclusive use of this approach for players’ metabolic
conditioning could conceivably affect motivation and compliance over time
due to the monotony of this form of training. In addition, the lack of sports
skill element and the fact that it features only straight-line running in a
forwards direction means that training of this type is highly unlikely to confer
any improvements in economy for other forms of game-related locomotion
and the various change of direction movements that feature in matches.
Repeated sprint conditioning
When interval training features maximal work intensities, this form of
training is more accurately defined as repeated sprint training (Billat 2001b). It
has been suggested that for clarity this term should only be used for protocols
employing maximal sprints of relatively short duration (that is, ≤10 seconds)
that involve minimal deterioration of work output within each sprint bout, as
opposed to longer, all-out efforts of 30 seconds or more, which would fall
under the bracket of the supramaximal interval training described above
(Girard et al. 2011a).
Relatively longer recovery durations are often employed with this form of
training, in order to allow more complete restoration of PCr stores within the
muscle (Billat 2001b). Protocols in the literature have employed recovery
intervals as long as 4 minutes between work bouts (Bodganis et al. 1996).
Depending on conditions, such as work intensity and nature of recovery
employed, rest intervals of this length allow almost complete restoration of
PCr stores within the muscle; this enables the contribution of the phosphagen
system to energy production to be maintained over consecutive sprints (Billat
2001b). The contribution of oxidative metabolism also increases with each
work bout, despite the near maximal work intensities and extended recovery
periods used in these protocols (Bodganis et al. 1996).
Some authors have suggested that repeated sprint conditioning over short
distances using work:rest ratios recommended to optimise PCr resynthesis
may be a suitable approach for developing the capacities required by team
sports players (Little and Williams 2007). Proponents of this approach have
suggested that the sprint distances and work:rest ratios recommended also
correspond quite closely to those reported for various field team sports.
A study has investigated a range of repeated sprint protocols with reference
to the physiological responses of soccer (Little and Williams 2007). Variations
of two protocols were used: 15 sets of 40m sprints with either 1:4 or 1:6
work:rest ratio; and 40 sets of 15m sprints, again with either 1:4 or 1:6
work:rest. Based upon physiological responses recorded the authors of the
study suggested that the 40x15m sprints with 1:6 work:rest ratio would be
most applicable to soccer (Little and Williams 2007). With both 15m and 40m
sprint distances the decrement in sprint times when 1:4 work:rest ratios were
employed was concluded to be too great for use with soccer players. However
the authors did also suggest that the 15x40m sprints with 1:4 work:rest might
have application as an overload training stimulus for soccer players (Little and
Williams 2007).
Performing maximal shuttle sprints has been investigated as an alternative
approach to repeated sprint training (Buchheit et al. 2010a). This involves
maximal efforts covering the same total distance but incorporating one or
more 180-degree turns; each bout is performed against the clock in the same
way as for the straight-line repeated sprint protocol. Due to the shorter
distances to attain top speed, and the need to decelerate to stop and turn,
sprinting speed is markedly lower when performing shuttle sprints compared
to straight-line sprints over the same total distance. Sprint times were
reportedly around 30 per cent worse (that is, higher) when performing 2 ×
12.5m shuttle sprints (one 180-degree turn) compared to 25m straight-line
sprints in a sample of senior team sports athletes (Buchheit et al. 2010a). In the
same study a variety of physiological indices were also higher under the
shuttle sprint protocol, indicating that repeated shuttle sprint conditioning is
also associated with greater physiological load.
Tactical metabolic training approach
The ‘special endurance’ approach to conditioning models training intensities
upon the workloads and the ‘effort distribution’ observed during competition
(Plisk 2000). In the case of sports featuring intermittent activity, a key
parameter for structuring conditioning is the work:rest ratios observed from
competition (Plisk 2000). The process of identifying relevant parameters from
competitive match-play in order to apply this data to players’ metabolic
conditioning has been termed ‘tactical modelling’ (Plisk and Gambetta 1997).
The tactical metabolic training (TMT) approach to conditioning is essentially
an extension of the high-intensity intervals and repeated sprint conditioning
approaches – the difference being that the intensity of work intervals and
work:rest ratios employed are directly based upon those observed during
competitive matches.
Such an approach gives recognition to the interrelationship between energy
systems during competition, as energy systems are trained in combination in a
way that aims to reflect the bioenergetics of competition (Plisk and Gambetta
1997; Plisk 2000). Proposed advantages of TMT include greater time efficiency,
as skill elements can be incorporated into metabolic conditioning (Plisk and
Gambetta 1997). This is favourable from a coaching viewpoint as it allows
technical and tactical elements to be executed in simulated game conditions,
and would likely also be advantageous in that it would engender greater
motivation and enhanced training compliance among athletes (Plisk and
Gambetta 1997).
The ‘special conditioning’ TMT approach for team sports was originally
developed in American football. This sport is highly structured with the ball
only being live for brief periods until the player in possession of the ball is
tackled or the ball goes out of play, at which time there are extended
stoppages until play restarts. As described in an earlier section, the majority of
team sports are less structured and feature highly variable patterns of activity,
which poses greater challenges to application of this approach. Objectively
quantifying competition demands tends to demand extensive analysis of
physiological and time–motion or GPS data, and this would also need to
reflect the respective demands placed on each playing position.
If these data are available for the sport in question, the application of the
TMT approach might be possible by structuring conditioning drills based
upon relevant data, such as work:rest ratios (Plisk 2000; Plisk and Gambetta
1997). Application of the TMT approach based upon work:rest ratios published
in the literature has previously been described for collegiate basketball (Taylor
2004); however, in general this approach is not widely employed as a
consequence of the logistical difficulties described.
Skill-based conditioning drills
As outlined there are significant methodological issues that compound the
inherent difficulty in collecting data to quantify demands associated with
team sports in general, and particularly collision sports. The complexities and
inherent variability of team sports renders efforts to design conditioning drills
to simulate match conditions all the more difficult (Gabbett 2002).
Furthermore, strength and conditioning specialists seek to not merely simulate
typical match-play demands, but rather impose overload in terms of the
intensity, frequency, duration and density of specific activities demanded in
match-play (Gamble 2007).
An alternative approach to provide appropriate overload is to employ skillbased conditioning drills that require the player to operate at the extremes of
frequency, duration and intensity of activity levels that they could expect to
experience during a competitive match.
Small-sided conditioning games
This approach to metabolic conditioning comprises purpose-designed games
involving reduced numbers of players on each team and featuring modified
playing areas and rules, which allows training intensity to be manipulated
(Hoff et al. 2002; Hill-Haas et al. 2011). The application of small-sided games
as a metabolic conditioning modality has been described for various team
sports, including soccer (Dellal et al. 2008), rugby union (Gamble 2004), rugby
league (Gabbett 2006), basketball (Castagna et al. 2011), handball (Buchheit et
al. 2009) and volleyball (Gabbett 2008). A variety of small-sided conditioning
games with different rules can be adapted from other ball games, while still
using the same regulation ball and similar skill set to that featured in the sport
for which the athlete is training (Gamble 2007b).
Depending on the choice of conditioning game and other related
parameters, it is possible to elicit different levels of training intensity. Factors
identified as influencing training intensity with conditioning games include
pitch dimensions, players per side and presence of coaching and/or instruction
(Rampinini et al. 2007b). Typically, the highest training intensities are
produced with small-sided games on a relatively larger playing surface (HillHaas et al. 2011). However, there does tend to be an optimal size of playing
area, in relation to numbers of players on each side, which requires greatest
exertion without allowing the player in possession too much time and space
(Jeffreys 2004). In general, lower player numbers are associated with the
greatest work intensity, with most studies reporting that the 2-versus-2 format
elicits the highest physiological responses (Castagna et al. 2011). Manipulating
player numbers so that there are uneven numbers on each team, for example
implementing a floating player who joins whichever team is in possession, is
another option for altering work intensity (Hill-Haas et al. 2011). Other rule
modifications that can influence demands placed on players include
restricting the time the ball is out of play (Hoff et al. 2002; Rampini et al.
2007b).
Hoff and colleagues (Hoff et al. 2002) concluded that small-sided games
fulfilled the necessary criteria to be an effective means of interval training for
soccer players, on the basis of HR and respiratory responses recorded during
training. A study of junior elite volleyball players likewise showed that the
skill-based conditioning game studied involved comparable time in specified
intensity zones (defined ranges of players’ percentage HRmax) as those
recorded when the players were engaged in competitive matches (Gabbett
2008). In support of this, a training study employing small-sided conditioning
games with young elite handball players reported significant improvements in
various measures of repeated sprint ability and aerobic capacity following
training (Buchheit et al. 2009). The application of small-sided conditioning
games during pre-season training for rugby league football players similarly
produced equivalent gains on measures of aerobic fitness to a control group
that performed interval running conditioning (Gabbett 2006). Similarly, in
rugby union football, a pre-season conditioning programme exclusively
employing conditioning games was shown to produce significant
improvements in cardiorespiratory responses to a standardised shuttle test
with elite-level senior players (Gamble 2004b).
Small-sided conditioning games are suggested to be a superior method for
metabolic conditioning based upon the specificity of this training mode
(Buchheit et al. 2009). For example, small-sided games require decisionmaking under fatigue and simulated game conditions, encompassing both
movement and context specificity (Gamble 2004b; Jeffreys 2004). This would
appear also to be a highly time-efficient and integrated approach, as smallsided games not only incorporate relevant sport skills and modes of
locomotion, but these skills and movement responses are also executed in
reaction to game-related cues, thereby providing concurrent development of
technical and tactical elements (Hill-Haas et al. 2011). The skill and
competition elements that are the key features of skill-based conditioning
games are suggested to promote enhanced effort despite the apparently lower
perceived exertion ratings by participating players (Gabbett 2006). As such the
skill-based conditioning games approach is likely to engender greater
compliance, making this form of conditioning amenable to continued use over
an extended period (Gamble 2007b; Jeffreys 2004).
The skill element that is a feature of conditioning games has been suggested
to offer concurrent sports skills development as it requires relevant sport skills
to be executed under game conditions and while fatigued (Gabbett 2006;
Gamble 2007b). A study of elite junior volleyball players reported that skillbased conditioning games conferred some improvement in scores for certain
sport skill measures, albeit they did not produce the degree of improvement
on the same range of measures as a training group that engaged in specific
skill practices (Gabbett 2008). Accordingly, this form of conditioning should
complement players’ skill work, but should not replace dedicated skill
practice.
There is also some indication that this approach to conditioning is
associated with lower injury rates, in comparison to other forms of training
(Gabbett 2002). Gabbett (2002) reported reduced rates of injury when rugby
league players were engaged in skill-based conditioning games, in contrast to
the far higher incidence of injury reported when performing traditional
conditioning (without any skill element) reported in this study. It is
conceivable that enhanced motor control when performing game-related
movements may be one factor responsible for the apparent decreases in injury
rates, in comparison to traditional running conditioning (Gamble 2004b).
One caveat with this approach is that a greater level of variability in
players’ physiological responses is reported with small-sided games, in
comparison to more structured conditioning such as high-intensity running
intervals (Dellal et al. 2008; Hill-Haas et al. 2011). Physiological responses and
movement patterns also appear to be influenced by the skill level and
technical abilities of the players performing this form of conditioning (Dellal
et al. 2011). There is also some suggestion that individuals with higher
endurance capacities may not receive the same training stimulus as other
players within the team when participating in small-sided games conditioning
(Hill-Haas et al. 2011).
The manner of delivery when conducting metabolic conditioning with
small-sided games, and the way in which players are monitored during these
sessions, would appear to be critical in terms of minimising variability in
players’ physiological responses both within and between training sessions.
Small-sided games with fewer players on each side appear to produce more
consistent work rates (Hill-Haas et al. 2008). If larger player numbers are used
it is recommended that the conditioning game is played on a correspondingly
larger pitch, so that the relative playing area per player is equivalent (HillHaas et al. 2011). It would also appear to be important that the teams for
small-sided conditioning games are selected carefully so that opposing teams
are well matched in terms of both playing ability and aerobic capacity. The
presence of the sports coach to provide verbal encouragement and instruction
when conditioning games are being conducted also appears to enhance the
consistency of players’ work rates over time (Rampinini et al. 2007b).
Training using such an inherently unstructured format as conditioning
games requires some objective marker to evaluate the work rates of individual
players (Gamble 2007). Heart rate (HR) monitoring is extensively used as the
most effective and practical means to objectively monitor intensity during a
training session (Potteiger and Evans 1995), and quantify training loads in the
athlete’s weekly training log (Gilman and Wells 1993). The use of HR to
monitor exercise intensity has also been validated against direct measurement
of ventilatory responses during small-sided conditioning games in soccer
players (Hoff et al. 2002). Monitoring of players’ HR therefore would appear a
crucial adjunct to the skill-based conditioning games approach, in order to
quantify training intensity in the conditioning game setting (Gamble 2007b). It
has also been suggested that the HR data recorded should be expressed as
percentages of players’ individual HRReserve, in order to reflect both maximum
and resting heart rate values for each player (Dellal et al. 2008). Providing
timely and appropriate feedback to players, ideally following each set or after
the training session, and based upon objective data, provides a means to
increase levels of compliance and ensure players work consistently at the
desired level of intensity.
Conclusions and training recommendations
High-intensity interval training and repeated sprint conditioning appear to be
the training approaches best suited for concurrent development of the
physiological and metabolic capacities required to prepare players for the
intermittent exertion that is characteristic of team sports. It is likely that a
blend of both these forms of training represents the best approach in order to
elicit adaptations across the full spectrum of factors that have been identified
as contributing to repeated sprint performance. Given the complex nature of
the metabolic requirements of team sports play, and the host of physiological
and neuromuscular factors described, it is perhaps unsurprising that there is
no single training approach that is optimal, and a mixed approach is likely to
be most effective (Bishop et al. 2011).
A range of different conditioning modes may be employed to provide highintensity interval training and repeated sprint conditioning. For example,
high-intensity interval conditioning may be undertaken using conventional
running conditioning, small-sided conditioning games, or any combination of
these two methods. Small-sided conditioning games might be viewed as
equivalent to ‘long’ aerobic interval training (set durations are typically in the
range of 2–8 minutes), whereas high-intensity running conditioning might be
employed for short intervals (for example, 30–15 second or 15–15 second
work:rest intervals). Likewise, repeated sprint training might feature a
selection of conventional sprints, shuttle sprints and maximal-intensity
conditioning drills featuring game-related movements. Finally, these
metabolic conditioning modes should be complemented with appropriate
speed development, strength and speed-strength training, in order to provide
concurrent development of speed and neuromuscular qualities (Bishop et al.
2011).
Each of these training modes has various strengths and limitations in terms
of specificity, practicality, physiological responses and issues of motivation
and compliance over time. A blend of these different approaches,
implemented strategically throughout the training year, would again seem to
be the best approach. Similarly, the selection of conditioning approaches and
prescription of intensity, volume and work:rest parameters should follow a
coherent progression, according to the periodised plan for the sport season
and the individual athlete.
5
STRENGTH TRAINING
Introduction
Specificity is manifested in both the ability of the athlete to express their
strength in a particular athletic movement and the nature of the training
response to a particular strength training intervention (Carroll et al. 2001).
Fundamentally, a player’s strength capabilities when lifting in the weights
room is of less relevance than their ability to express that strength when
executing athletic and skilled movements on the field of play. How training
effects ultimately transfer to sports performance therefore represents a
primary consideration when designing a strength training programme.
The obvious application of specificity with regard to the outcomes of
strength training is exercise selection. Particular modes of strength training
have greater transfer of training effect in terms of what performance effects
are manifested, based upon the mechanics and kinetics of the training exercise
(Stone et al. 2000a). Strength training outcomes are also dictated by the
particular combination of strength training variables employed. Training
intensity, repetition scheme and volume all interact to determine the specific
strength training response (Baechle et al. 2000). These factors in turn influence
the nature of the training response elicited with respect to different strength
qualities – for example, maximum strength versus strength-endurance (Young
2006).
In turn, the requirement for a particular strength quality for a team sports
player will depend on the typical demands placed upon them during
competition. It follows that sport-specific and position-specific considerations
should be addressed in the design of strength training, in order to develop the
required combination of strength qualities for the sport and playing position.
The final consideration for strength and conditioning specialists is that
strength training design should also be specific to the needs of the player.
From this viewpoint a starting point in attempts to tailor a programme for a
player might include musculoskeletal and movement profiling, in combination
with a battery of performance tests to identify any areas in need of particular
attention.
Requirements and relevant strength qualities for team
sports
There is currently a lack of contemporary strength testing data published from
professional team sports players; the studies that have been published mainly
concern contact team sports. Scores on strength and power measures are
shown to distinguish elite professional players in collision sports from those at
lesser levels (Baker 2001b, 2001d). This asserts the importance of developing
strength properties for contact sports such as rugby football – in fact it
appears to be a prerequisite for participation at the highest level (Baker 2002).
There is a significant progression reported in these strength qualities at
each stage from high-school level, through college age, to senior professional
level (Baker 2002). Independent of any difference in lean body mass, elite
professional rugby league players are able to express greater upper-body
strength and power than semi-professional and college-aged players (Baker
2001b, 2001d). Upper- and lower-body power measures of elite rugby league
players are shown to be heavily dependent on their levels of strength (Baker
and Nance 1999a). Given the observed importance of strength and lean body
mass, it is thus crucial to maximise the effectiveness of the strength training
players are able to perform within the constraints of other training and team
practices.
In collision sports such as American football and rugby football, physical
size and muscularity confer an advantage to the player during contact
situations. Accordingly, body mass and size of players in these sports have
risen disproportionately in recent times. It is reported that over a 25-year
period the body mass and levels of mesomorphy of top-level rugby union
players has shown consistent increases at five times the rate of that seen for
the general population in the same period (Olds 2001). Individual players are
similarly predisposed to, and selected for, particular playing positions on the
basis of their anthropometric characteristics and strength capabilities (Quarrie
et al. 1995; Quarrie and Wilson 2000; Duthie et al. 2003). Site-specific
hypertrophy is also important in contact sports such as American football and
rugby football (Kraemer 1997). The shoulders are a key area for development
as this is frequently the point of impact when tackling opponents.
Based upon what data exist in the literature, there appear to be significant
differences in strength demands between playing positions in the sports
studied. For example, it has been identified that different playing position
groupings in professional rugby league vary in their performance on various
strength, speed and endurance measures (Meir et al. 2001). Specifically, rugby
league forwards exhibit greater upper-body strength than backs. Conversely,
outside backs in rugby league are faster over 15m than forwards – and faster
than all other positional sub-groups over 40m (Meir et al. 2001). All playing
positions, irrespective of differences in body mass and positional demands,
require high levels of dynamic muscular strength relative to body mass in
order to contend with the physical aspects of the sport (Baker 2001b; Meir et
al. 2001).
When athletes are required to perform movements repeatedly, other
capabilities are implicated that relate to the strength qualities described.
Strength-endurance, speed-endurance, and power-endurance are identified as
discrete elements and should be considered independently, as opposed to
merely derivatives of strength, speed and power (Yessis 1994). The capacity to
activate musculature under conditions of fatigue has been identified as a
trainable quality (Behm 1995). Under conditions of fatigue, trained individuals
appear to have superior ability to fully activate the musculature (Behm 1995).
Two key adaptations identified as underlying strength-endurance are acid–
base buffering (Kraemer 1997) and neural mechanisms (intramuscular coordination) that make the athlete better able to more fully activate fatigued
motor units (Behm 1995).
Sport-specific strength
Strength training has become established as a key component in a programme
of physical preparation for the majority of sports. However, the diverse
physical demands involved in team sports pose unique demands for strength
training design. For the majority of sports it is suggested that athletes require
optimal levels of strength as opposed to maximal levels in order to
successfully compete in their sport (Murray and Brown 2006). It is therefore
important to recognise that ‘optimal strength’ may be a more important
training goal than maximal strength for these athletes. The design of strength
training should therefore reflect the specific demands of the particular sport –
and in the case of team sports, the playing position.
What defines ‘sport-specific’ strength capabilities is the ability of the player
to express their strength qualities during the execution of game-related
activities or sport skills in the context of a match situation (Smith 2003).
Anecdotally, many coaches will be familiar with the scenario that their top
performing players are not necessarily those that have the best strength test
scores or lift the heaviest weights in the weights room (McGill 2006d). One
aspect of this is that team sports performance requires more than just strength
performance. However, another implication is that the strength and speedstrength capabilities expressed in the context of team sports are somewhat
different to the classical weights room definition of strength performance.
Fundamentally, strength and conditioning specialists cannot lose sight of
the fact that they are preparing the athlete to perform on the field – not to
increase the athlete’s strength test results for their own sake. Strength tests
may show some correlation to performance, playing level or selection in
certain sports. However, the focus should remain on building athleticism to
allow the athlete to compete in their sport, not to convert the athlete into a
powerlifter. Strength test scores may well improve – preferably in those tests
that resemble the demands of the sport – but this is secondary to improving
athleticism and the athlete’s ability to express functional or sport-specific
strength. The ultimate measure of the success of the athlete’s programme is
the extent to which it improves their performance in the field of play, not in
the weights room. Transfer of training effects is a crucial factor: one of the key
criteria when judging the efficacy of a strength training programme is the
degree of performance improvement relative to the training time invested
(Young 2006).
Associated benefits of strength training for team sports
players
Reducing risk of injury
Sport-specific physical conditioning can favourably influence injury risk when
playing team sports. One general protective effect is that appropriately
conditioned athletes are more resistant to neuromuscular fatigue, which
renders athletes susceptible to injury (Hawkins et al. 2001; Murphy et al. 2003;
Verrall et al. 2005). This is illustrated in the common trend observed in many
team sports for higher injury rates in the latter stages of matches when
players are fatigued (Best et al. 2005; Brooks et al. 2005a; Hawkins and Fuller
1999; Hawkins et al. 2001). Strength training also serves a general protective
effect in making the musculoskeletal system stronger and thereby more
resistant to the stresses incurred during games (Kraemer and Fleck 2005). The
addition of strength training to the physical preparation of male collegiate
soccer players was followed by an almost 50 per cent reduction in injury rates
during subsequent playing seasons (Lehnhard et al. 1996). One aspect of this is
that trained muscle is more resistant to the microtrauma caused by strenuous
physical exertion and also recovers faster (Takarada 2003).
In addition to the general benefits of strength training and metabolic
conditioning, targeted interventions have the potential to specifically guard
against certain injuries to which athletes may be exposed. Injury preventionoriented strength training employs particular exercises specifically designed to
address certain risk factors and injury mechanisms associated with a
particular type of injury in the sport. This application of specific training
interventions, of which strength training is a key component, is discussed at
length in Chapters 9 and 10.
Strength training to improve endurance performance
Neuromuscular aspects that can influence players’ endurance performance
can be developed via appropriate strength training. Neuromuscular factors
that contribute to endurance performance include neural and elastic
components of stretch-shortening cycle capabilities, intermuscular co-
ordination influencing running mechanics and movement economy, and also
the strength qualities of locomotor and postural muscles (Paavolainen et al.
1999). Improving these aspects independently of any changes in aerobic or
anaerobic endurance parameters has the potential to improve endurance
performance (Mikkola et al. 2007, Millet et al. 2002b, Paavolainen et al. 1999).
Such beneficial effects of strength training on parameters of endurance
performance have been demonstrated in athletes in various sports. A number
of studies of endurance athletes report that time trial performance is improved
by the addition of strength training to their physical preparation, and these
improvements occur independently of any changes in physiological
parameters such as VO2max scores (Mikkola et al. 2007, Millet et al. 2002b,
Paavolainen et al. 1999). Accordingly, a recent study showed that strength
training intervention was effective in producing improvements in measures of
endurance and repeated sprint ability with team sports players (Buchheit et al.
2010d).
The force-generating capacity of the locomotor muscles and the ability to
maximally recruit these muscles during conditions of fatigue are important
factors when engaged in endurance activities (Paavolainen et al. 1999). It
follows that improving strength, speed-strength and strength-endurance
should positively influence economy and performance when engaged in
endurance activities. In addition, neuromuscular control and co-ordination
aspects influence the stiffness and elasticity of the muscle–tendon complex
during foot strike when running (Paavolainen et al. 1999). For example,
increases in measures of lower limb muscle stiffness were shown following a
period of strength training in elite triathletes (Millet et al. 2002b). Improving
such capacities via appropriate strength and speed-strength training can
increase the non-contractile contribution to work output during locomotion.
Reducing energy cost of locomotion in this way will improve movement
economy and thereby improve endurance capacity (Millet et al. 2002b). Given
that team sports feature a variety of modes of locomotion in multiple
directions, it follows that selection of strength-training exercises should reflect
this in order to confer such improvements in movement-specific work
economy.
Approaching strength training for team sports players
A number of the practices and conventions observed in athletic preparation –
in particular with regard to strength training – have evolved from competitive
powerlifting, weightlifting and bodybuilding (Fleck and Kraemer 1997). This
should be recognised when evaluating and designing strength training
programmes for team sports. It is important that strength and conditioning
specialists are able to discern between practices, even at the level of exercise
selection, that are based predominantly on convention as opposed to those
that serve a specific purpose with regard to players’ physical preparation for
the sport.
A survey investigating the practices of strength and conditioning coaches in
US Division One collegiate competition revealed that what most influenced
their training design and prescription was the input and practices employed
by their peers (that is, other collegiate strength coaches) (Durell et al. 2003). In
contrast, only 9 per cent of these collegiate strength and conditioning coaches
ranked journals or books as their primary information source when designing
programmes. Similar surveys of professional North American team sports did
not include this question. However, responses of strength and conditioning
coaches in National Football League, National Hockey League, Major League
Baseball and National Basketball Association indicated similar reliance on
convention and non-scientific sources with respect to different aspects of
training programme design and implementation rather than evidence-based
practice (Ebben and Blackard 2001; Ebben et al. 2004, 2005; Simenz et al. 2005).
All team sports feature common fundamental movement abilities to some
degree: these include gait and locomotion (for example, running), squatting
and/or lifting, pushing and/or pulling, lunging, twisting and maintaining
balance (McGill 2006c). A logical starting point for a strength training
programme is to address any deficiencies or areas of weakness that restrict the
player’s ability to efficiently execute these fundamental athletic movements.
From a performance viewpoint, a player can be deemed to be only as strong as
the weakest link in the kinetic chain from the supporting lower limb to the
limb which is executing the movement. This kinetic chain may extend from
the supporting foot to the upper limb, for example when executing a throwing
or striking movement. Lack of mobility and deficits in strength or function at
any one of the integrated system of joints in the kinetic chain will ultimately
limit performance, as well as potentially causing pain and injury.
Traditional approaches to training can serve to strengthen areas where the
athlete is already strong without addressing the weak links that will
ultimately limit performance. Without corrective training, this has the
potential to make the athlete more imbalanced and place tissues around any
weak links under further strain. The approach and the strength training
modes that are most appropriate will therefore depend upon the constraints of
the individual. For example, the barbell back squat is an exercise that is
employed year-round as the cornerstone of the strength programme for some
sports. Based upon electromyographic (EMG) data recorded from muscles
during the classical barbell back squat, this lift can be categorised as primarily
an exercise for the quadriceps muscles – at least for the majority of the
exercise range of motion (McGill 2006b). The back squat is a good option if the
aim is improving general strength of the knee extensors. However, an
emphasis on the back squat in the training for an athlete who already exhibits
quadriceps dominance and weak gluteal muscles might in fact exacerbate this
dysfunction and further predispose the athlete to injury and impaired
performance.
Similarly, selection of exercises should reflect the programme goal for the
training phase. Consideration should be given to specificity with respect to
transfer of training effects, as well as the capabilities of the athlete. For
example, if the primary aim of the strength-training programme is producing
gains in speed capabilities in the short term, bilateral strength training modes
such the back squat would not represent the best option for a player who
already exhibits adequate maximum strength levels (Young 2006). For
example, an 8-week strength training intervention with the back squat
exercise reported this training mode to be highly effective in improving back
squat 1-RM strength (21 per cent gain) and vertical jump performance (21 per
cent); however, very limited improvement (2.3 per cent) was seen in sprinting
speed (Wilson et al. 1996).
A recent trend in the strength and conditioning industry and the field of
athletic preparation has been the growth of ‘functional training’ approaches,
which are often employed to the exclusion of conventional heavy resistance
training methods. This approach ignores the longer-term implications of
training adaptation and the size principle of motor unit recruitment, and is
therefore very unlikely to produce consistent gains in performance. The
paradox of specificity and transfer of training effects was discussed in Chapter
1. Whilst highly task-specific modes offer a high degree of dynamic
correspondence, by their nature these training modes are unable to provide
the levels of force required to elicit the requisite adaptations that will
ultimately optimise performance (Bondarchuk 2007). For example, the
maximal loading the standing cable press is able to provide is reportedly only
40.8 per cent of the athlete’s body mass (Santana et al. 2007). The loading
provided by common functional training exercises and sport-specific training
modes is therefore typically insufficient to recruit high-threshold motor units
and elicit the gains in strength and produce the morphological adaptations
that are the prerequisites for the development of athletic performance.
Conversely, heavy resistance training modes impose the loading conditions
required for mechanical and morphological adaptations that underpin
strength and power performance. However, as illustrated in the previous
study investigating the transfer of heavy resistance training modes to speed
performance (Wilson et al. 1996), employing these methods in isolation will
also not confer the desired improvements in athletic performance. It follows
that the optimal approach to strength training is likely to feature a blend of
training modes that span a continuum, ranging from heavy resistance training
modes to highly sport-specific training.
Specificity of dose–response
strength training experience
relationships
with
Training experience is a key consideration for strength-training prescription:
there is an obvious need to progress intensity, volume and frequency of
training, as the neuromuscular system grows more accustomed to strength
training with increased exposure (Rhea et al. 2003). Exercise prescription
guidelines accordingly make a distinction in terms of resistance training
experience and feature separate recommendations for untrained,
recreationally trained and advanced lifters (Kraemer et al. 2002). Metaanalysis of the strength-training literature demonstrates that training
responses vary depending on subjects’ training status (Rhea et al. 2003). Thus
the levels of intensity, volume and training frequency shown to maximise
gains differ based upon the training experience of the subject population
(Peterson et al. 2004). It appears logical that individuals with different training
experience will require different ‘doses’ of training parameters in order to
elicit a maximal training response, in terms of strength gains.
Such dose–response relationships with regard to optimal resistance load,
volume and frequency of strength training have previously not been identified
in competitive athletes. There is a paucity of data from elite team sports
athletes in particular – for example, the absence of contemporary data
concerning strength levels of elite players in rugby union football has been
highlighted (Duthie et al. 2003). However, one study has undertaken a metaanalysis of 37 studies in the strength training literature that directly examined
athlete subjects (Peterson et al. 2004). Summarising the findings of these
studies, the authors found that the training parameters that optimise training
effects (measured strength gains) in competitive athletes differ from those
based on similar studies employing strength-trained non-athletes. Training
volume (sets per muscle group), training frequency (days per week for each
muscle group) and training intensity (resistance load) found to be most
effective in the studies examined differed markedly from those for nonathletes – even non-athlete subjects experienced in strength training (Peterson
et al. 2004).
Hence, competitive athletes show different dose–response relationships
with regard to strength training in comparison even to strength-trained nonathletes (Peterson et al. 2004). From these studies it appears that a continuum
exists in terms of optimal training variables for maximal strength gains, which
is dependent on the training status and training experience of the individual
(Rhea et al. 2003) – and that elite athletes appear to sit further along this dose–
response continuum (Peterson et al. 2004). As such, elite team sports players
are shown to require considerably different intensity, frequency and volume
of strength training to maximise strength gains (Peterson et al. 2004).
This consideration raises questions regarding the relevance of findings in
the strength-training literature based on investigations involving non-athletic
populations, even using subjects with strength training experience (Peterson et
al. 2004). The lack of studies denies any opportunity for comparison of the
current findings to existing data. There remains a critical need to gather data
pertaining specifically to athletes, in particular those engaged in team sports.
Obtaining access to elite athletes is likely to require some compromise in
terms of study design (Millet et al. 2002a). However, only in this way will it be
possible to provide an objective alternative to the ongoing tendency of
strength and conditioning coaches working in many team sports to rely upon
their own observations and personal experience as the primary basis for
selection of training modes and methods (Kraemer 1997).
Strength training prescription for elite athletes
The specific needs of competitive athletes are vastly different from those of
recreationally trained individuals: it is logical that by extension the optimal
training for athletes will likewise be different. On this basis, elite performers
should be treated as a special population (Cronin et al. 2001b). Maximal
strength gains are demonstrated in untrained individuals training at an
average intensity of 60 per cent 1-RM (repetition maximum), whereas
individuals experienced with strength training exhibit maximum gains with
80 per cent 1-RM resistance; competitive athletes appear to exist further still
along this continuum. From what data are available, some suggestions for
training prescription applicable to team sports players can be made: a mean
training intensity of 85 per cent 1-RM has been found to have greatest effect
in competitive athletes from the majority of relevant studies (Peterson et al.
2004). This equates to an average intensity of 6-RM (that is, the greatest
weight that can be lifted for six repetitions with proper form).
This is in general agreement with the finding that loads greater than 80 per
cent 1-RM were necessary to maintain or improve strength throughout the
playing season in college American football players (Hoffman and Kang 2003).
Observation of elite weightlifters likewise noted a significant decrease in EMG
recorded during the phase of the training year when training intensity
dropped below 80 per cent 1-RM, which recovered once training intensity was
increased above 80 per cent in the subsequent training period (Hakkinen et al.
1987). This requirement for greater average intensity appears to be a common
theme for athletes as a special population. Of all training variables, training
intensity was the only significant predictor of strength changes during an inseason period in college American football players (Hoffman and Kang 2003).
Training studies featuring protocols in which the athlete subject group lifted
to failure report greater average strength gains (Peterson et al. 2004).
Therefore, it appears there is a need for strength training regimes to stipulate
the athlete must exert maximal effort at the specified load, as training at lesser
intensities appears to elicit minimal improvements in competitive athletes
(Hoffman and Kang 2003).
In terms of frequency of strength training, recommendations are based on
the number of times per week individual muscle groups should be trained.
From data examining athletes, training a particular muscle group two or three
days per week was observed to be similarly effective (Peterson et al. 2004).
How many strength training sessions this equates to will depend on the layout
of the workout. It could be two workouts per week in the case that both days
are whole-body sessions. On the other hand, if a ‘split routine’ format is being
used (for example separating upper- and lower-body workouts), this may
comprise four or more strength-training sessions per week. There is some
evidence that a 5-day programme incorporating split routine loading may
offer greater strength and muscle mass gains (Hoffman et al. 1990). However,
given the time constraints imposed in many team sports, the former 2- or 3day whole body format may be more time-efficient during the majority of the
season.
Recommendations for volume of strength training for competitive athletes
are similarly made in terms of individual muscle groups. A mean number of
eight sets per muscle group per week appears to maximise strength gains in
groups of athletes (Peterson et al. 2004). This represents double the equivalent
volume recommendations based on studies for non-athletes: the majority of
studies employing non-athletes found four sets per muscle group per week to
be effective in evoking maximal strength gains (Rhea et al. 2003). Competitive
athletes thus appear to require a much greater volume of strength training to
provide an effective training stimulus for gains in strength. Similarly, players
in contact sports for whom hypertrophy is a programme goal require greater
training frequencies to elicit the necessary gains. It has been identified that
quite extreme training frequencies (four and five days per week) are required
to elicit body mass gains in college-aged American football players
experienced in strength training (Hoffman et al. 1990; Kraemer 1997). These
distinct differences in optimal training volumes again reinforce the specific
needs of competitive athletes as a special population.
Strength and conditioning specialists must, however, be careful with what
constitutes an ‘advanced athlete’ with respect to strength training. Most
players will have strength training experience to the extent that they have
been engaged in some form of resistance training for a period of time.
However, despite – or potentially as a result of – having been resistance
trained for a number of years, an individual player may still exhibit deficits in
mobility, stability and/or imbalances in strength that impair their ability to
perform fundamental athletic movements. Following a neuromuscular skillbased approach to strength training, training status and therefore the starting
point for the individual player’s strength training programme will depend
upon an assessment of their functional movement abilities alongside their
scores on strength, power and performance tests. Similar ongoing qualitative
assessment of the player’s neuromuscular skill and movement abilities can
likewise be used to help govern the rate of progression in their strength
training programme.
Format of strength training
Another application of specificity, which is typically not fully accounted for,
is the format in which strength training workouts are performed. Team sports
involve a wide array of movements in multiple directions executed repeatedly
in an unspecified order with high force. Contact field sports feature the added
element of movements executed against resistance, often with the upper body
as the point of contact. For team sports players, the optimal training format
has yet to be adequately investigated. Anecdotally, some strength and
conditioning specialists working with professional team sports players attempt
to address this by incorporating the use of ‘compound sets’ – that is,
alternately performing sets of one exercise (for example, a pushing lift) with
another exercise (such as a pulling lift).
Taking this approach further, a circuit format might be considered for the
entire workout. This should not be mistaken for traditional circuit training
which features submaximal loads and relatively high repetitions; the same
loads are used: it is solely the format of the workout that is altered. The circuit
format would also appear to have the advantage of reducing workout time (as
players will move onto the next lift in the interval during which they would
normally be resting) and potentially stimulating improvements in strengthendurance. A study investigating this approach termed this method ‘heavy
resistance circuit training’ and found that subjects were able to lift the same
load and volume with no alternation in bar kinematics compared to the
traditional sequential format, and that it also elicited a greater cardiovascular
response (Alcaraz et al. 2008). The authors concluded this approach to strength
training could be expected to elicit similar strength improvements with
additional cardiovascular benefits.
A subsequent study has confirmed the efficacy of strength training
performed in a ‘heavy-resistance’ circuit format. An 8-week training
intervention with resistance-trained subjects produced similar improvements
in strength (bench press and squat 1-RM) and bench throw power output
scores, and gains in lean mass to subjects who trained with the traditional
strength format (Alcaraz et al. 2011). The session duration for the high
resistance circuit format was significantly shorter, and there were also
additional improvements in body composition that were not observed with
the traditional strength-training group (Alcaraz et al. 2011). The latter finding
corresponds to the greater cardiovascular response previously reported with
this training format (Alcaraz et al. 2008). An earlier study by Kraemer (1997)
reported improvements in strength-endurance (number of repetitions the
subject was able to complete at 80 or 85 per cent 1-RM) with American
football players following a multi-set strength training at 8–12RM, performed
in a circuit fashion. This was attributed in part to improvements in lactate
buffering and whole body acid–base balance associated with the circuit
format (Kraemer 1997).
It has been shown that with adequate rest (3 minutes) between sets, RM
loads can be lifted repeatedly (Kraemer 1997). The crucial factor influencing
capacity to repeatedly perform sets at RM load was identified as rest period
between sets. When rest is reduced, ability to perform the prescribed number
of repetitions at the RM load may be compromised (Kraemer 1997). The
sequential approach of lifting the prescribed sets for one lift before moving on
to the next exercise may lead to insufficient rest between sets to successfully
complete the stipulated repetitions with the RM load. Players typically selfselect rest between sets and may rush through the sets in an effort to perform
all the exercises within the limited time allotted for the workout. The circuit
format described avoids this, as the muscle groups involved in a particular lift
are allowed to rest while the player completes the intervening exercises in the
circuit prior to performing next set.
Strength-training methods and modes
The particular constraints of a given training mode serve to determine the
stimulus provided to the neuromuscular system in terms of intra- and intermuscular co-ordination (Carroll et al. 2001). In this way, biomechanical
aspects that include the kinematic and kinetic profile of a particular strengthtraining exercise will influence the degree to which there is any direct transfer
of training effects to a given aspect of neuromuscular performance in the
short term (Newton et al. 1999). This concept has been termed dynamic
correspondence.
The method employed for applying resistance during strength training is
accordingly a key factor that influences the neuromuscular stimulus provided.
For the majority of multi-joint training movements, free weight application of
resistance has generally been considered to be more functional as the lifter is
required to stabilise their own body and the external resistance, while
simultaneously controlling and directing the movement (Kraemer et al. 2002;
Stone et al. 2000b). For example, free weights exercises develop intra- and
inter-muscular co-ordination to a greater degree than training with
conventional weight-stack resistance machines. This is reflected in greater
strength gains and superior transfer to athletic and ergonomic performance
measures in comparison to machine-based resistance training (Stone et al.
2000b).
A number of other methods for applying resistance and novel strength
training practices have emerged with the growth of the strength and
conditioning industry. The strength and conditioning specialist is therefore
faced with a variety of options, depending on access to the appropriate
equipment. These options range from suspension training methods whereby
the player’s own body weight provides the resistance, to highly specialised
devices including variable resistance machines and pneumatic resistance
training modes. In addition, bands, ropes and chains have been employed to
provide variable resistance when performing conventional free weights
training exercises.
There is currently very little data to support manufacturers’ claims
regarding the superiority of these devices and equipment for athletic
development. In general, most devices restrict the motion and in turn the
degrees of freedom of the strength-training exercise; the mechanical and
associated neural stimulus provided therefore does not correspond to the
conditions encountered during normal activities (Frost et al. 2010). It has
similarly been suggested that manipulating the resistance provided at different
points in the exercise range of motion with the use of bands or chains alters
the kinetic and kinematic profile of the strength-training mode in an artificial
manner that may not produce appropriate adaptation in neural co-ordination
when related movements are performed under ‘real-world’ conditions during
competition (Frost et al. 2010).
Conversely, cable pulley devices employing either weight-stack or
pneumatic resistance offer a means to provide resistance in a variety of
directions. One limitation with isoinertial free weights exercises is that by
definition the forces applied are dictated by the acceleration due to gravity,
which acts only in a downward vertical direction.
The majority of game-related movements in team sports are executed
partly or fully from a single-leg base of support. It follows that unilateral
support exercises should necessarily comprise a significant portion of the team
sport athlete’s training (McCurdy and Conner 2003). Unilateral strength
training was reported to be similarly effective in producing improvements in
strength and vertical jump performance in comparison to bilateral strength
training in a study of untrained subjects (McCurdy et al. 2005). Unilateral
support exercises also do not allow the athlete to favour their dominant limb
during the movement as can occur with bilateral lifts (Newton et al. 2006). For
example, differences in force production have been observed between
dominant and non-dominant legs in collegiate female softball players when
performing the bilateral barbell back squat exercise (Newton et al. 2006). The
number of sets and/or repetitions can also be manipulated to increase the
training stimulus provided to the weaker side. Unilateral support exercises
offer a means to address such imbalances in strength between limbs. This is
important both in terms of function and performance, but also from an injury
prevention perspective in view of the reported association between strength
and flexibility imbalances with injury incidence (Knapik et al. 1991).
Similarly, upper-body movements in team sports are typically unilateral. It
follows that training to develop players’ upper-body strength and power
should feature an appropriate emphasis on alternate arm and single arm lifts.
Such exercises also require greater stabilisation of the trunk, as the unilateral
resistance results in destabilising torques that must be compensated for by the
trunk muscles on the opposite (contralateral) side (Behm et al. 2005). This
stabilising challenge corresponds to what occurs during match-play, hence
can be viewed as beneficial in terms of transfer of training effects.
The quantity of muscle mass involved in the training exercise, as well as
frequency and volume load (repetitions multiplied by mass lifted) of training
will influence adaptations in body composition (Stone et al. 2000a). Free
weight exercises that recruit a large amount of muscle mass have greater
metabolic demand and hormonal responses, which tends to favour alterations
in body composition. This is important for contact team sports in which
developing high levels of lean muscle mass are a key programme goal. Similar
considerations underpin recommendations for multiple-joint free weights
exercises recruiting large muscle mass to develop local muscular endurance
and strength-endurance (Kraemer et al. 2002).
Progression of strength training variables
There is a need for progressive increases in training stress applied as training
advances to achieve continued adaptation. Even the best designed programme
will not produce significant gains over time without continuing to take the
neuromuscular system beyond what it is accustomed to. Progressions in
training intensity may be achieved by increasing force demands, either by
increasing mass lifted or increasing the acceleration at which the movement is
executed (or any combination of these two variables). Progression can
likewise be achieved by manipulating volume load via repetitions performed,
training volume (number of sets and exercises in the workout) and/or training
frequency (weekly number of sessions per muscle group) (Kraemer et al.
2002). Finally, the neural stimulus with respect to intra- and inter-muscular
co-ordination requirements provided by the strength-training intervention
represents another option for achieving progression. With increasing training
experience and as training status advances, more challenging training regimes
and more sophisticated manipulation of training parameters are required to
elicit a training response (Newton and Kraemer 1994; Kraemer et al. 2002).
Progression of strength training modes: the specificity
continuum
Manipulating exercise selection to progress the neuromuscular and motor
control demand, in a systematic and sequential manner over time, provides
not only progression but also facilitates transfer of training effects from
preceding training phases. It is important not to ignore the role of training
adaptations elicited by preceding training cycles, in terms of building the
athlete’s capabilities for the training scheduled in successive training cycles, as
this will also ultimately determine the longer-term training effects observed at
the culmination of the training macrocycle (Bondarchuk 2007). When taking
account of specificity and transfer of training effects, consideration must
therefore be given not only to the direct effects observed in the short term, but
also to the indirect long-term effects on the player’s capabilities that will
ultimately be reflected in performance improvements if progression is used
appropriately. This principle is the central tenet of the study of the transfer of
training effects and the staged model described by Bondarchuk (2007).
For example, strength training implemented early in the training year
might feature heavy resistance training modes designed to maximise increases
in force-generating capacity and produce adaptation in both contractile
elements and connective tissues. Once this foundation development has been
completed early in the training year, successive training cycles might then see
a shift towards more technically demanding lifts and those that require
greater balance and stabilisation. This sequential progression in exercise
selection might then culminate with the most specific training modes which
show a high degree of dynamic correspondence to the movements performed
in the sport being employed towards the end of the competition season, in
order to facilitate the greatest short-term transfer of training effects.
Manipulating neuromuscular demands in this way as a means to achieve
progression is in keeping with the alternative approach to strength training for
team sports characterised by a neuromuscular emphasis that was described
previously. Given that it is motor control rather than gross strength
capabilities that commonly separates the best performers in many team sports
(McGill 2006d), it follows that the means for achieving progression when
designing players’ strength training should reflect this.
General strength development
As discussed in a previous section, traditional heavy resistance training modes
provide the most potent means to elicit mechanical and morphological
adaptation that are the prerequisites for optimal development of strength and
power. As such, exercise selection during the general strength development
phase will feature conventional ‘powerlifting’ training modes, for example
barbell squat and deadlift. However, alternative training modes that demand
greater co-ordination and provide additional development of postural strength
will also have a role during this phase. For example, the front racked variation
of the barbell squat exercise is shown to elicit comparable levels of muscle
recruitment to the conventional back squat, with lesser compressive loads,
which may be important for those players with a history of lower limb injury
(Gullet et al. 2009).
The front squat also has apparent benefits in terms of developing sound
technique: essentially it is very difficult to perform this lift without
maintaining proper technique simply due to the constraints of the exercise.
Specifically, the fact that the barbell rests on the front of the shoulders means
that in order to execute this lift the athlete must control their posture and
maintain form through the full range of motion, otherwise they risk losing the
bar. Equally, once sound technique has been developed, the conventional back
squat should not be neglected during this phase, as it allows greater loads to
be handled and has proven efficacy in terms of developing strength (Wilson et
al. 1996).
In addition to bilateral heavy training modes, exercise selection should also
comprise unilateral heavy resistance training modes. Issues of dynamic
correspondence remain a consideration even during the general development
stage, which favours the use of training modes that feature a unilateral base of
support for team sports players’ strength development. Crucially, a study that
compared muscle activity and hormonal responses during unilateral versus
bilateral strength-training modes reported that a version of a free weight
resisted single-leg squat (termed a ‘pitcher squat’ in that study) produced
similar values for muscle activation and post-exercise testosterone
concentrations in trained college-level athletes (Jones et al. 2012). These
findings support the use of unilateral barbell exercises for heavy resistance
training.
Figure 5.1 Barbell single-leg squat
One unilateral strength training mode that would appear to have a
particularly important role in the strength training of team sports players is
the barbell step up exercise. This training mode has been identified as eliciting
marked activation of the hip musculature during both concentric and
eccentric phases of the exercise (Simenz et al. 2012). For example, the levels of
activation of gluteus maximus during a 6-RM step up onto an 18-inch
(45.75cm) box are considerable during both eccentric and concentric phases,
and markedly greater than the values reported for the squat exercise. From a
biomechanical viewpoint, this exercise also represents a closed kinetic chain
movement that comprises simultaneous hip and knee extension executed from
a unilateral base of support, which is reflective of jumping and locomotion
movements that feature during competition.
Transition strength training modes
Often there is a dichotomy in the training modes employed with athletes:
general or ‘nonspecific’ heavy resistance training modes are often combined
or immediately followed with highly specific training modes and ‘functional
training’ practices. In order to achieve a coherent and stepwise progression in
terms of exercise selection, there is a clear need to consider the intermediate
training modes that exist between these two extremes of the specificity
continuum. It follows that ‘transition’ strength training modes should
therefore be implemented during the training blocks that follow the general
preparation phase and precede the highly specific training employed during
the middle and latter stages of the playing season. This approach is analogous
to the specialised preparatory and specialised developmental cycles described
in the staged model described by Bondarchuk (2007).
Figure 5.2 Barbell step up
The transition training modes implemented to fill this void will essentially
be variations and progressions of conventional strength training modes. There
will be an increasing emphasis on specificity and dynamic correspondence
with respect to the exercise modes employed in each successive training block.
From this viewpoint, there will be an increased emphasis on unilateral modes
for lower limb strength training. Likewise, exercise selection should feature a
progression in terms of the neuromuscular co-ordination and postural stability
challenge imposed. To this end, front racked variations of barbell resisted
unilateral support strength-training exercises might be considered, in a similar
way as described in the previous section with the bilateral barbell squat
exercise.
Another key factor with respect to exercise selection will be the direction of
force application. Whereas the bilateral and unilateral lower limb strengthtraining modes featured in the general strength development block comprised
the application of vertical ground reaction forces, exercise selection during
this phase should also account for the horizontal ground reaction forces that
are a feature of locomotion activities. Similarly, there will necessarily be a
shift from predominantly sagittal plane movements to training modes that
feature movements in a variety of directions. For example lateral, diagonal
and crossover variations of the lunge and step up exercise have been described
in the literature. An investigation of the loaded step up exercise performed on
an 18-inch (45.75cm) box that employed lateral, diagonal, and cross-over
versions of this exercise reported that the respective variations produced
different levels of activation of the hip muscles studied, which included
gluteus maximus and medius, biceps femoris and semitendinosis, and rectus
femoris, vastus medius and vastus lateralis (Simenz et al. 2012). Each of these
variations and progressions would appear to merit consideration during this
phase.
Figure 5.3 Front racked barbell diagonal lunge
Figure 5.4 Barbell lateral step up
Exercise selection for upper limb strength development during this phase
will similarly feature variations of conventional strength training modes. For
example, alternate arm variations of standard upper-body strength training
exercises with dumbbells provide a strength training stimulus that is
combined with a stabilisation challenge for the lumbopelvic region and
shoulder girdle. It has previously been reported that single limb versions of
resisted upper limb strength training exercises with dumbbells (Behm et al.
2005) and cable resistance (Tarnanen et al. 2012) elicit significant activation of
various stabiliser muscles of the trunk.
‘Transfer’ strength training
As implied, exercise selection during this phase places the greatest emphasis
on dynamic correspondence. Hence there will be a further progression in
terms of the specificity continuum, and the training modes selected will
favour the greatest immediate transfer to movements in the sport.
Accordingly, the strength training exercises employed in this phase will be the
most challenging in terms of co-ordination and stabilisation demands. The
versions of conventional lower limb strength training modes that feature will
thus comprise the most challenging overhead variations (Figure 5.6), and
exercises involving movements in multiple directions (Figure 5.7).
Similarly, strength training modes for the upper limbs will feature exercises
performed in a weight-bearing stance. Single-arm variations of resisted upper
limb movements in various directions will likewise feature. As such, upper
limb strength training modes selected will recruit muscles of the upper and
lower limbs, as well as comprising considerable activation of the trunk
musculature to resist destabilising torques and maintain ‘postural integrity’
(Fenwick et al. 2009; Santana et al. 2007).
Figure 5.5 Alternate arm incline dumbbell bench press
Figure 5.6 Barbell overhead step up
Figure 5.7 Dumbbell clockwork lunge
Figure 5.8 Alternate arm cable fly
Figure 5.9 Single-arm cable row
Conclusions and training recommendations
Given the time constraints imposed by extended playing seasons and high
volumes of concurrent training and team practices common to all team sports
at elite level, the efficiency and effectiveness of physical preparation is
paramount (Peterson et al. 2004). One of the key criteria when evaluating a
strength training programme for a team sports player is the degree of
improvement in the player’s capacity to perform and remain fit to participate
in matches and team practices versus the training time invested (Young 2006).
This need to optimise any strength training performed is particularly
important given the potential for interference effects from concurrent
metabolic conditioning (Leveritt and Abernethy 1999) – and in the case of
contact sports particularly, the disruption due to the physical stresses of bodily
contact during practices and matches (Hoffman and Kang 2003). Such
complications place even greater emphasis upon the effectiveness and
efficiency of strength training for team sports players.
In this chapter a neuromuscular emphasis has been described for
approaching strength training for team sports. Whatever the sport or training
history of the player, the initial programme goal suggested is addressing any
deficits in mobility and stability that have been identified that impair the
player’s ability to effectively perform fundamental athletic movements. Once
this foundation is established, exercise selection should progress towards
integrated multi-joint movements, which are specific to movements that are
characteristic of the sport (Baechle et al. 2000; Stone et al. 2000a). Accounting
for specificity in this way will benefit gross motor activation or intramuscular
co-ordination as well as enhancing inter-muscular co-ordination and local
neural control at in a way that facilitates transfer to performance (Sheppard
2003; Young 2006).
Progression of exercise selection within the strength training macrocycle
might feature a gradual introduction of unilateral support lifts, as well as
alternating upper limb and single limb variations of strength training
exercises – in order to increase balance, stabilisation and neuromuscular
control demands. Similarly, speed-strength and plyometric exercises that
involve similar progressions can be introduced into players’ preparation,
particularly as they approach key phases in the playing season. In this way,
acceleration can be manipulated as a way of progressing intensity in the
players’ programme. From a specificity viewpoint, it follows that these speedstrength exercises should also be executed in a manner that corresponds to the
rate of force development associated with competition (Sheppard 2003) and
features inter-muscular co-ordination demands appropriate to the sport
(Young 2006).
In terms of the format of strength training for team sports players, strength
and conditioning specialists might consider experimenting with the structure
of the workout. Manipulations to the traditional set configuration for Olympic
lifts (adopting short rest intervals between consecutive repetitions) have
proven to reduce impairments in lifting kinematics in successive repetitions in
a set, by reducing residual fatigue (Haff et al. 2003). It is possible that the
circuit format may allow similar enhanced lifting kinematics by offsetting
fatigue between consecutive sets of a particular exercise. There is also early
evidence that such an approach might increase cardiovascular responses
(Alcaraz et al. 2008) and confer similar benefits in terms of strengthendurance (Kraemer 1997), as well as reducing the time required to complete
the workout.
In general the strength and conditioning specialist should adopt a
neuromuscular training emphasis with respect to maintaining the focus on the
quality of movement during strength training rather than solely load lifted.
Such a neuromuscular skill-focused approach would appear to make sense
given that it is commonly motor control rather than gross measures of
strength or power that distinguishes the best athletes from their peers (McGill
2006d); and this is the case particularly in team sports. In this sense, rather
than coaching by numbers and focusing on improving loads lifted, the players
should be instilled with the principle that if they are unable to lift a given load
with perfect form then they cannot lift it. In keeping with this approach,
measures to facilitate maintaining posture and form, and offset the effects of
acute fatigue, should be considered – for example breaking a set up into
smaller chunks (particularly during the initial stages after load has been
increased). This is analogous to the use of cluster sets – a practice employed
by Olympic weightlifters and which has been suggested to have applications
for other athletes (Haff et al. 2003, 2008).
6
TRAINING FOR POWER
Introduction
Expression of power is determined by the constraints of the task and
phenomena characteristic of the neuromuscular system, such as the force–
velocity curve and muscle length–tension relationship (Cormie et al. 2011a).
Several discrete aspects of the neuromuscular system that influence power
output have been isolated (Newton and Kraemer 1994; Newton and Dugan
2002). These individual neuromuscular components involved in expression of
explosive power can be considered trainable; developing each of these
components either in isolation or in combination can favourably impact upon
expression of power (Newton and Kraemer 1994). Developing each of these
neuromuscular factors that contribute to explosive power expression in turn
requires an appropriate training stimulus specific to the respective component.
Training specificity is evident when training to develop ‘explosive power’
or speed-strength. It has been identified that the neuromuscular firing patterns
observed during strength-oriented and explosive movements are grossly
different (Ives and Shelley 2003). Neuromuscular firing patterns and intramuscular co-ordination demands are accordingly key factors which
differentiate training methods which are effective for developing explosive
power from other forms of strength training (Young 2006).
Speed-strength training comprises a special category of training modes that
fulfil the requisite conditions to develop explosive power production. Speedstrength training modes have a demonstrated capacity to impact specifically
upon explosive performance (for example, jump-and-reach height)
independently of any changes in other strength properties such as maximum
strength (Newton et al. 1999; Winchester et al. 2008).
Aside from considerations regarding neuromuscular firing patterns and
intra-muscular co-ordination, in much the same way as strength training
exercises, transfer of speed-strength training methods to sports performance is
also determined by the dynamic correspondence of the training mode to the
sports movement. Speed-strength training therefore must likewise satisfy
kinetic, kinematic and biomechanical criteria related to the athletic or sport
skill movement in order to be most effective.
Approaching training for power or ‘speed-strength’
There have historically been differing schools of thought regarding the best
training approach for developing explosive muscular power. It has been
suggested by some that it is sufficient to solely develop force-development
capabilities (that is, strength) and then transfer the gains in strength by
subsequent practice with the particular athletic activity (Kraemer 1997). Such
an approach essentially accounts for the force element in the force × velocity
equation for power. However, explosive power is a learned motor skill of the
neuromuscular system and is identified as a capacity that is distinct from
maximal force production (Ives and Shelley 2003). Although maximal power
output is dependent upon strength to a varying extent depending on the
resistance involved (Stone et al. 2003a), expression of sport-specific power has
elements that are independent of the basic force-generating capacity of the
musculature. This is illustrated by the dissociation of maximum (1-RM)
strength and explosive power scores in elite athletes (McBride et al. 1999;
Delecluse et al. 1995).
The efficacy of specific training to develop power is demonstrated by the
observed improvements in measures of explosive power performance with
short-term speed-strength training interventions in the absence of any
maximal strength gains (Newton et al. 1999; Winchester et al. 2008). Likewise,
Olympic lifts have been found to increase concentric power (squat jump
height) in elite strength athletes (champion weightlifters) (Hakkinen et al.
1987). This is similarly significant, as traditional heavy resistance training
modes are relatively ineffective in developing lower-body power (vertical
jump height) in trained power athletes, despite significant concurrent gains in
1-RM strength (Baker 1996).
Such considerations led to the genesis of a multidimensional construct for
explosive muscular power. Several discrete elements of the neuromuscular
system have been isolated, all of which influence power output (Newton and
Kraemer 1994; Newton and Dugan 2002). Each of these individual components
of the neuromuscular system that contribute to expression of power can be
considered trainable. ‘Mixed methods’ training strategies propose employing a
range of training modalities to specifically train each neuromuscular capacity
implicated in the expression of explosive power (Newton and Kraemer 1994).
These factors, targeted via appropriate training, have the potential to
individually contribute to the development of explosive power capabilities.
Developing these components in combination can further have a cumulative
impact upon the athlete’s ability to develop explosive power.
Evidence as to the efficacy of mixed methods training is seen by the
superior results elicited by combination training in comparison to either highforce or high power training (Harris et al. 2000). Greater gains are reported
with strength-trained team sports players (collegiate American football
players) on a wider range of performance measures following a combination
of both high-force and high-velocity ‘power’ training. Performed individually,
high-force training effects are limited to gains in maximal strength (1-RM)
and heavy load speed-strength (hang pull 1-RM) measures, with no impact on
dynamic athletic measures. Conversely, the high-velocity ‘power’ training
resulted in gains in dynamic measures, with no change in heavy load
capabilities (Harris et al. 2000). Interestingly, combination training not only
yielded the benefits associated with both single training modes, but also
produced gains on measures (10-yard shuttle agility run and average vertical
jump power) not seen with either high-force or high-velocity training alone
(Harris et al. 2000). Adaptation to high-force or high-velocity training
performed in isolation by strength-trained athletes are restricted to the region
of the force–velocity curve that characterised the training. Furthermore,
combined methods are observed to be most effective in developing vertical
jump height (the standard measure of lower-body power production) (Baker
1996). Superior performance effects on a broader spectrum of the force–
velocity curve with combined training were attributed to exploiting different
avenues of explosive performance development simultaneously (Harris et al.
2000).
Factors in the expression of explosive muscular power
The individual elements that have been implicated in the expression of
explosive muscular power will be discussed in turn.
Maximum dynamic strength
In accordance with the force–velocity curve, maximum strength is developed
at slow movement velocity. This strength quality is nevertheless required at
the initiation of any explosive movement to overcome inertia when system
velocity is zero or slow (Stone 1993). Maximum strength therefore has a major
influence on the initial rate at which force is developed early in the movement
(Stone et al. 2003a). For locomotion and jumping movements in particular,
even in the absence of external resistance, there is a significant inertia
component due to the athlete’s own body mass. This inertia component is
particularly significant if there is any change of direction involved, as the
athlete’s own momentum in the original direction of movement must first be
halted and overcome in order to generate movement in a new direction.
Accordingly, maximum strength relative to body mass is a key element in
expression of power for gross motor actions involved in a variety of athletic
movements (Peterson et al. 2006). High correlations are observed between 1RM strength and power output even for unloaded jumps. Furthermore, slow
velocity strength development influences the mechanical power output a
player is able to generate in higher resistance regions of the load/power curve
(Stone et al. 2003a). For players in contact sports in particular, the ability to
generate power against external resistance is an important factor, which
similarly relies heavily upon high levels of force output and therefore
maximum strength.
Rate of force development
Rate of force development (RFD) describes the ability to develop force within
a limited timeframe. This component represents the slope of the force–time
curve for a muscular action (Newton and Dugan 2002). The time interval for
force development in many athletic movements is very brief – typically
within 300ms (Newton and Kraemer 1994). On this basis some authors
identify RFD as possibly the most important capacity influencing athletic
performance (Wilson et al. 1995). Accordingly, RFD is associated with the
ability to achieve rapid acceleration for a given movement (Stone 1993).
Rate coding is identified as a major factor influencing RFD; specifically the
maximal firing rates of motor units within the window for force development
allowed by the movement (Behm 1995). Motor unit recruitment is another
critical factor: the ability rapidly to recruit high-threshold motor units
associated with the highest force-generating capacity and power output is
directly related to maximal power development. For rapid contractions that
occur during ballistic activities, the threshold of motor unit activation is
relatively lower than for slow graded contractions (Cormie et al. 2011a). It
follows that training modes which feature ballistic contractions will be
favourable for developing this capacity.
It also follows that the duration of the concentric portion of the training
exercise must be similarly brief to train the neuromuscular system to develop
maximal force across the shorter timeframes permitted by rapid athletic and
sports skill movements. In support of this it is reported that the closer the time
interval of a given strength measure to the contact time observed for athletic
movements, the greater the correlation to performance (Young et al. 1995).
Similarly, on this basis traditional heavy strength training would appear to be
suboptimal for developing this RFD component. For example, a heavy barbell
squat can take around 1.5–2 seconds to complete (Baker 2001b). Conversely,
motor unit firing rates are appreciably higher during the short window for
force development associated with maximal ballistic concentric actions
(Hedrick 1993; Behm 1995). Under certain conditions improvements in
isometric RFD have been noted following isometric training in non-athlete
subjects (Behm and Sale 1993); however, the relevance to athletic performance
of both isometric training (Morrissey et al. 1995) and isometric measures of
RFD (Wilson et al. 1995) has been questioned.
High-velocity strength
High-velocity strength represents the ability to exert force at high contraction
velocities. Increasing maximum strength at slow movement velocity is of
limited relevance if the athlete is unable to express this greater forcegenerating capacity at the movement velocities encountered during athletic
and sports skill movements (Hedrick 1993). This ability is in part determined
by anatomical and mechanical factors associated with muscle fascicle length.
In particular, more sarcomeres in series will serve to share the overall muscle
fibre shortening between a greater number of subunits, so that the rate of
shortening at the level of the individual sarcomere will be less for a longer
muscle fascicle (Cormie et al. 2011a). In turn, this reduced shortening velocity
at sarcomere level will allow more force to be developed. Muscle fascicle
length is determined to a large degree by genetic factors. However, there may
be scope for chronic adaptive responses to training that may include increases
in muscle fascicle length and/or the addition of more sarcomeres in series
(Cormie et al. 2011a).
The neural basis for improvements in force development at higher velocity
regions of the force–velocity curve include adaptations relating to the capacity
of motor units to fire rapidly for short intervals (Hedrick 1993) and may also
include the preferential recruitment of high-threshold motor units (Stone 1993;
Cronin et al. 2001a). Such adaptations in intra-muscular co-ordination appear
to result in specific improvements at the higher movement velocity region of
the force–velocity curve (Stone 1993). Improvements in high-velocity strength
may also include changes at the level of the muscle fibre. Adaptations in the
contractile properties of muscle fibres that lead to increased maximal
shortening velocity and peak power have been shown to be elicited by
appropriate training (Malisoux et al. 2006).
Stretch-shortening cycle capabilities
The majority of movements in sport involve some kind of pre-stretch or
countermovement which serves to increase force and power output for the
concentric portion of the movement (Cormie et al. 2011a). This increase in
power output originates from the interaction between muscle and tendon
structures during the transition between eccentric and concentric action,
referred to as the stretch-shortening cycle. The stretch-shortening cycle (SSC)
comprises not only mechanical aspects associated with the contractile
(muscle) and connective tissue structures, but also neural aspects including
reflexes at local spinal level.
Authors increasingly distinguish between ‘fast SSC’ (100–200ms) and ‘slow
SSC’ (300–500ms) movements based upon the duration of ground contact or
force application. Changes in SSC performance are found to be relatively
independent of maximal muscle strength in highly trained athletes (Plisk
2000). The contribution of SSC to concentric power output in part depends on
the capacity of the musculoskeletal complex to store and use elastic tension
(Yessis 1994; Newton et al. 1997). As such, mechanical adaptations that alter
the compliance of these structures may contribute to improved concentric
power output (Cormie et al. 2011a).
In addition to mechanical adaptations that alter the passive properties of
connective tissue structures, changes in active stiffness are also apparent
following exposure to SSC movements due to changes in muscle activation
which modify the interaction between muscle and tendon during these
activities. In the case of bounding movements, the ‘fast SSC’ contribution to
concentric power output can also be modified via changes in neural input in
the interval prior to and during ground contact. Such modification in
descending neural input to the muscles from higher motor centres is
responsible in part for the improvement in fast-SSC performance following
appropriate training (such as plyometrics).
Another component of the underlying neural mechanisms that may
contribute to augmenting concentric power output immediately following
pre-stretch is associated with the ‘stretch reflex’. This is a peripheral reflex at
local spinal level that acts to stimulate the stretched muscle to contract, in an
attempt to return the muscle to its previous length (Potach and Chu 2000).
This stretch reflex-mediated neural drive is superimposed upon voluntary
drive to the agonist muscles, which leads to augmentation of power output in
the subsequent concentric phase (Newton et al. 1997).
Neuromuscular skill and co-ordination
The final component of explosive power is neuromuscular skill. In much the
same way as sport-specific strength, a player’s effectiveness is limited to the
extent that they are able to express the elements of explosive power described
above during the execution of game-related activities and sport skills at the
decisive time in match situations (Smith 2003). This encompasses both intermuscular and intra-muscular co-ordination (Newton and Kraemer 1994).
Broadly, intra-muscular co-ordination comprises the recruitment and firing
of motor units of muscle groups involved in the movement. Intra-muscular
co-ordination thus encompasses descending neural drive from the motor
cortex and excitatory and inhibitory inputs originating from local spinal level
(Cronin et al. 2001b). Increasing motor unit recruitment, descending neural
drive and net excitatory input to the motor units involved in an athletic or
sports skill movement will have a favourable effect on force and power
output. The constraints of the task will largely dictate what is required in
terms of intramuscular co-ordination. For example, a key aspect of intramuscular co-ordination in the context of power expression is the ability to
develop force within the time window allowed by the athletic or sports skill
movement (Cormie et al. 2011a).
Inter-muscular co-ordination concerns the co-ordinated action of muscles
that are involved in producing athletic or sports skill movements (Young
2006). The interaction between agonist, synergist and antagonist muscle
groups employed during a particular movement is highly complex and entails
both the magnitude and timing of activation (Cormie et al. 2011a). Increasing
force or power output of a single muscle group in isolation could conceivably
impair athletic performance if the increased single muscle function is not
achieved in co-ordination with other muscle groups acting on the kinetic
chain of joints involved in a movement. Inter-muscular co-ordination
therefore comprises both the timing of activation and also relaxation of
muscles involved in producing movement in order to allow fluid and rapid
motion (Cormie et al. 2011a). For example, one important adaptation in intermuscular co-ordination is reduced co-contraction of agonist and antagonist
muscle groups, which allows for greater angular velocity and torque
development (Newton and Kraemer 1994).
Inter-muscular co-ordination is a critical factor for the relatively ‘gross’
motor skills involved in athletic movements. In the case of fine motor skills
involved with sports skill movements, such as throwing and striking, the
ability to co-ordinate motion between joints and limbs of the kinetic chain
involved in the activity assumes even greater importance with respect to
movement velocity and power output. For example, the one-handed overarm
throwing skill that features in sports such as baseball, cricket and netball is
described in terms of multiple linked segments operating in series, comprising
lower limbs, pelvis, trunk, shoulder and upper limb, with motion ultimately
translated to the finger tips and imparted upon the ball. The degree and
relative timing of the sequential motion of these segments is identified as
critical to torque generation and efficient throwing mechanics (Aguinaldo et
al. 2007).
Inter-muscular co-ordination does not only concern the limbs generating
force and producing the movement. A characteristic double peak pattern
associated with activation of the trunk musculature is observed during
striking and kicking movements (McGill et al. 2010). The contract-relaxcontract sequence includes a preparatory pulse to stiffen the core to provide a
strong base from which to accelerate the limbs to initiate the striking action,
followed by a relaxation phase to allow fluid and rapid whole-body motion,
prior to a second ‘pulse’ timed to stiffen the body again as the limb strikes the
target. It follows that adaptations in inter-muscular co-ordination will be
closely related and highly specific to the particular movement(s) featured in
training (Young 2006).
Speed-strength training modes for development of
explosive muscular power
Conventional strength training provides a means to develop maximum
strength and provide the requisite foundation development that will
ultimately confer the ability to express explosive muscular power with the aid
of subsequent specific training. Strength training therefore serves a critical
role in the long-term development of power capabilities. Without this baseline
development of force-generating capacities, as well as the morphological and
neural adaptations that are produced by heavy resistance training, the athlete
will not be able to generate high levels of muscular power. Athletes therefore
require optimal levels of strength – developed via appropriate heavy
resistance training – as a precursor to training to specifically develop power.
The specific approach that may be taken to strength training has been covered
in a previous chapter. In support of this, there is evidence that improvements
in power output following speed-strength training (ballistic resistance
training) are greater in stronger subjects (Cormie et al. 2010a). That said, it
should be noted that the ‘weaker’ subjects in this training study did also
respond positively to the speed-strength training intervention.
Following this initial foundation development there remains a need for
specific speed-strength training in order to develop the specific ability to
express explosive muscular power. Accordingly, the addition of speedstrength training has been shown to produce gains beyond those elicited by
heavy resistance training alone (Newton et al. 1999; Baker 1996; Delecluse et
al. 1995). Speed-strength training modes have been identified as the optimal
means to develop a number of the qualities identified that underpin explosive
power expression. As implied by their title, speed-strength exercises combine
both high force (the product of mass and acceleration) and high velocity
(Hydock 2001). Speed-strength exercises are characterised by maximal rates of
force development (Hedrick 1993) throughout the movement range of motion
(Stone 1993). These power development-oriented exercises have thus been
termed ‘full acceleration’ exercises by some authors (Baker 2003).
Potential adaptations to speed-strength training include improvements in
contractile elements – such as increased maximum shortening velocity and
power output of muscle fibres (Malisoux et al. 2006). Speed-strength training
is also associated with preferential hypertrophy of high-threshold type II
muscle fibres (Stone 1993). Intent is key to the neural adaptations associated
with speed-strength training (Behm and Sale 1993). Due to their explosive
nature, speed-strength exercises are more suited to evoke explosive intent. In
the case of conventional strength training lifts such as the bench press, aside
from mechanical considerations, athletes also must be coached to make a
conscious effort to lift with explosive intent to optimise training responses on
explosive power scores (Jones et al. 1999). Velocity gains following training
are reportedly reduced by half when subjects are left to self-select lifting speed
(Jones et al. 1999).
Olympic weightlifting training modes
Olympic lifts are classified as speed-strength exercises (Stone 1993), on the
basis that they feature both a force (strength) and speed component (Hydock
2001). These lifts are unique in that the resistance is accelerated up the natural
line of the body and gravity acts to decelerate the load, which means the
neuromuscular system does not have to intervene to brake the motion of the
barbell (Kraemer 1997). Elevating the athlete’s own centre of mass represents
a significant component of the work done when performing Olympic lifts
(Garhammer 1993). In contrast to ballistic resistance training modes in which
the load is released at the end of the movement, with Olympic weightlifting
movements the external load (typically a barbell) is held throughout: in the
event that the barbell is still travelling upwards at the termination of the
concentric phase, the lifter’s feet merely come off the floor.
Applications
Average mechanical power output values reported for the Olympic lifts are
3,000W for the barbell snatch and 2,950W for the clean, which are nearly three
times greater than for back squat or deadlift (approximately 1,100W) (Stone
1993; Garhammer 1993). Peak power output recorded during the ‘second pull’
phase can be five times greater (5,500W) (Stone 1993). Peak propulsion forces
for these lifts are similarly comparable to those during jumping movements
(Stone 1993).
The unique nature of Olympic lifts allows heavy loads to be handled in an
explosive fashion (McBride et al. 1999). This enables high-force ‘speedstrength’ and rate of force development (RFD) elements to be developed
simultaneously. Olympic weightlifters exhibit equivalent strength scores and
superior dynamic power scores to powerlifters, which reflects the combination
of heavy loads and high velocity of movement featured in Olympic lift
training (McBride et al. 1999). That said, Olympic weightlifters do also
perform classic strength-oriented lifts in their training, which contributes to
their strength development. Olympic lifters are reported to generate greater
velocity and power than powerlifters when performing countermovement
jumps with or without added loading (McBride et al. 1999).
Similarly, Olympic lifters exhibit superior strength (1-RM squat) in
comparison to sprinters (McBride et al. 1999). From these data it could be
inferred that Olympic lift training is similarly effective to sprint training and
more effective than powerlifting training in developing dynamic power, and
more effective than sprint training in developing maximal strength. Similarly,
of particular relevance to contact team sports is the observation that Olympic
lifters perform better than sprinters in dynamic movements against resistance
(McBride et al. 1999). The superior performance exhibited by Olympic lifters
in this capacity suggests that the heavy load speed-strength training provided
by Olympic lifting has the potential to develop this ability to generate power
against resistance. Such observations point to the potential benefits of heavy
load speed-strength training, and specifically the use of Olympic lifts for
rugby football and other contact sports. However, controlled prospective
studies are required to draw definitive conclusions.
The kinetic and kinematic specificity of Olympic lifts with regard to the
vertical jump movement are suggested to develop speed-strength in a way
that transfers more readily to jumping performance (Baker 1996). A study of
semi-professional rugby league football players also reported that players’
scores on hang power clean relative to body mass discriminated between
those who showed superior performance on vertical jump and 20m sprint, as
well as speed-strength measures with a loaded jump squat (Hori et al. 2008). A
previous study with similar subjects reported hang power clean scores relative
to body mass to be significant predictors of acceleration (10m) and short
distance (40m) sprint scores in rugby league players (Baker and Nance 1999b).
In accordance with this a study using non-athlete subjects reported that shortterm (8 weeks) training using Olympic lifts in combination with heavy
resistance training improved both squat jump and countermovement jump,
and 10m sprint scores – although 30m performance was unchanged (Tricoli et
al. 2005).
The relative load used is shown to influence the power output with which a
lift is executed. Taking the hang power clean as an example, peak and average
power output varied with loads from 50 per cent to 90 per cent of subjects’
recorded 1-RM for the hang power clean (Kawamori et al. 2005). One
characteristic that makes Olympic weight-lifting movements unique is that
the relative loading at which mechanical power is optimised is relatively
higher than for other strength and speed-strength training exercises, including
ballistic resistance training modes. This may be favourable from the viewpoint
of activating high-threshold motor units, in accordance with the size principle
of motor unit recruitment (Cormie et al. 2011b). Peak and average power
output were reported to be maximised at the 70 per cent 1-RM load for the
hang power clean, albeit peak power output values did not vary dramatically
across a range of loads in this study (Kawamori et al. 2005). A more recent
study that measured peak power for both the barbell and athlete’s body mass
identified that peak power for the body + barbell ‘system’ is maximised at 80
per cent of squat 1-RM for the power clean (McBride et al. 2011).
Figure 6.1 Barbell split jerk
Selection of training loads will also depend in part upon the team sport in
question. For example, relatively lighter loads may be appropriate for sports
such as volleyball and basketball. Conversely, relatively higher loading
towards the 90 per cent 1-RM value might be preferred for collision sports,
such as rugby football and American football, given the need to overcome
external resistance provided by opposing players in these sports (Cormie et al.
2011b). In either case, a range of loads may be used during the course of
periodised strength and speed-strength-oriented training cycles.
Olympic lifts combine strength, power and neuromuscular co-ordination
elements in a way that favours transfer to athletic activities, such as vertical
jump performance (Kraemer et al. 2002). Peak propulsion forces relative to
body mass generated during the power clean lift are shown to be similar to
those exerted during jumping movements (Stone 1993). Likewise, Olympic
lifting movements involve a comparable time interval for force production,
typically between 100–200 milliseconds for the second pull phase (Garhammer
1993). On the basis of their biomechanical similarity and comparable
timeframes for concentric force production, Olympic lifts are routinely used in
athletes’ physical preparation as a means to replicate sport-specific
movements (Souza et al. 2002).
Mechanisms
The majority of the Olympic weightlifting exercises feature predominantly
concentric force and power production. During rapid concentric actions such
as those occurring during Olympic weightlifting movements, the muscle
shortens throughout the concentric phase, so that the majority of the
shortening of the musculo-tendinous unit occurs at the muscle fascicle rather
than the tendon (Kawakami et al. 2002). Underlying mechanisms for the gains
in concentric power output are generally ascribed to improvements in rate of
force development (RFD) and high-velocity strength (Stone 1993; Garhammer
1993; McBride et al. 1999; Souza 2002). Increased peak RFD has been reported
with concurrent gains in Olympic lift (snatch) 1-RM and performance test
(shot put distance) scores (Stone et al. 2003b). Both inter-muscular and intramuscular co-ordination elements are implicated in the training responses
observed (Newton and Kraemer 1994; Hedrick 1993). Potential adaptations in
inter-muscular co-ordination include improved recruitment of high-threshold
(high-force) motor units, enhanced co-ordination of synergist muscle
activation and reduced co-contraction of antagonist muscles.
Developments in intra-muscular co-ordination are manifested in both
recruitment of high-threshold motor units and enhanced capability of
individual motor units to fire rapidly for short intervals (Hedrick 1993). Other
aspects of adaptation in intra-muscular co-ordination are neuromuscular
learning effects associated with rapid muscular contractions (Morrissey et al.
1995). Such learned ‘neural strategies’ include over-riding inhibitory input and
an anticipatory priming of agonist motor units during the interval
immediately prior to initiating the movement (Baker et al. 2001d).
Limitations
Most Olympic lifts – particularly the pulling lifts – develop concentric power
output (Hakkinen et al. 1987), as opposed to stretch-shortening cycle (SCC)
components. Observations of a year’s weightlifting training in elite
weightlifters registered significant improvements in unloaded and loaded
squat jump height in the absence of any significant change in
countermovement jump height (indicative of ‘slow SSC’ performance) with
equivalent loads (Hakkinen et al. 1987). Similarly, these athletes also exhibit
very small differences between squat jump and countermovement jump
scores, indicating limited SSC augmentation of jumping performance (Baker
1996).
Although Olympic weightlifting training is consistently shown to improve
vertical jump performance, there is some uncertainty as to whether bilateral
speed-strength training of this type will transfer to sprinting performance
(Young 2006). A number of studies have failed to show improvements in
sprint scores even when improvements in jump height and performance on
other tests were seen (Harris et al. 2000). A training study with collegiate
football players that included derivatives of the Olympic lifts (mid-thigh pull
and push press) failed to show improvements in 30-metre sprint scores –
although improvements in jump height and performance on a stair climb
power test were seen (Harris et al. 2000). A more recent study, also examining
collegiate football players, compared Olympic lift training to powerlifting
training and likewise showed no changes in 40-yard sprint or T-test change of
direction performance in either group (Hoffman et al. 2004).
Change of direction performance also appears to be both independent of
hang power clean test scores (Hori et al. 2008) and similarly unresponsive to
training involving standard weightlifting movements (Hoffman et al. 2004;
Tricoli et al. 2005). This may be a consequence of the bilateral nature and
predominantly vertical force production that is characteristic of the classical
weightlifting movements. That said, single-leg and split variations of the
Olympic lift movements do exist that may transfer more readily to a broader
range of athletic and sports skill movements.
Limitations imposed by technique flaws in the catch phase when employing
the classical Olympic lifts can potentially restrict the load players are able to
handle (Hydock 2001). The pull variations of the Olympic lifts allow higher
loads (≈110–120 per cent) to be handled relative to the classical clean and
snatch lifts, which tend to be more limited by deficiencies in lifting technique
(Hydock 2001). The clean pull variation has the same biomechanical
characteristics of the power clean lift (minus the catch phase) and comprises
the maximal power second pull portion of the lift (Souza et al. 2002). Likewise,
the snatch pull also features the second pull phase, and power outputs during
the second pull for the snatch and clean are found to be very similar
(Garhammer 1993). Purely in terms of concentric power production, the
‘catch’ phases that characterise the classical Olympic snatch and clean lifts are
of little consequence (Hydock 2001).
The pull variations of these lifts are a good option for introducing Olympic
lifts into players’ training for speed-strength development and to allow
technique for the key ‘second pull’ phase to be developed. Furthermore, these
lifts will allow relatively higher loads to be handled than would be the case
for the full clean or snatch lifts, particularly for those players who are less
technically proficient. For both these reasons it is suggested that the pull
variations of the Olympic lifts might be the best option when the player
initially moves into speed-strength-oriented training phases in their training
macrocycle.
Ballistic resistance training
Ballistic resistance exercises represent one of the other major speed-strength
training modalities for developing concentric power capabilities. This form of
training is unique in that the load is released or projected into free space at the
end of the movement. It is this characteristic that makes ballistic resistance
training superior to conventional strength-training exercises in developing
elements of explosive muscular power (Cronin et al. 2003). Specifically,
ballistic resistance exercises allow power to be generated throughout the full
range of motion, as there is no requirement to brake the motion of the load to
bring it to a halt at the end of the movement. As the acceleration phase is not
terminated before the end of the range of motion (ROM) for the exercise, this
in turn allows higher velocities to be produced with the result that a higher
peak velocity (hence peak power) can be attained later in the movement
(Newton et al. 1996). Accordingly, Cronin and colleagues identified projection
(that is, release) of the load as the most crucial factor influencing expression of
peak power (Cronin et al. 2003, 2001a). This is reflected in greater average and
peak velocities observed with upper body movements for a range of loads (30–
60 per cent 1-RM) under conditions where the load is projected into free space
(Cronin et al. 2003).
Figure 6.2 Barbell split clean
Conventional strength training modes are unsuitable for speed-strength
training. Attempting to use traditional strength training exercises in an
explosive fashion (lifting the load as rapidly as possible, keeping hold of the
barbell at the termination of the movement) has been shown to be
counterproductive (Newton et al. 1996). Lifting lighter ‘maximal power’ loads
(45 per cent 1-RM) in this manner results in a significant deceleration
component, which can be up to 40 per cent of the range of motion (Newton et
al. 1996). As a result, in the case of the bench press, beyond the initial 10 per
cent of the range of motion at the initiation of the concentric movement, both
force and velocity are less than the corresponding values for the ballistic
bench throw at equivalent loads (Newton et al. 1996). This is accompanied by
a loss of motor activity in agonist muscles, reflected in reduced EMG recorded
for the bench press versus bench throw movement at these loads (Newton et
al. 1996).
Antagonist co-contraction is likewise increased when explosively
performing the bench press exercise, particularly with light loads (Cronin et
al. 2001a). As a result, the training stimulus is compromised for the affected
portion of the movement (Cronin et al. 2001a). Furthermore, efforts to lift a
submaximal resistance with maximal acceleration results in the barbell
gathering considerable kinetic energy, which will ultimately have to be
absorbed by the muscles and joints at the end of its range of motion (Newton
and Kraemer 1994). Attempting to use conventional strength training
exercises in this manner therefore engenders the risk of injury.
Applications
Jump squats have been identified as an effective training modality for
developing measures of lower-body explosive power (vertical jump height) in
elite power athletes (Newton et al. 1999; Wilson et al. 1993; Baker 1996). Shortterm (5 weeks) jump squat training was also reported to produce significant
improvements in high-force speed-strength measures (power clean 1-RM) in
collegiate American football players (Hoffman et al. 2005). Such changes in
speed-strength and vertical jump performance appear to be relatively
independent of changes in 1-RM strength and peak force measures or changes
in muscle morphology. A recent study examining performance effects and
underlying mechanisms for training adaptations with jump squat training in
recreational athletes reported significant gains in peak power, rate of force
development and peak velocity (Winchester et al. 2008). However, there were
no significant changes in peak force, 1-RM squat or muscle fibre type
expression accompanying these improvements in speed-strength measures.
The obvious upper-body equivalent to the jump squat is the bench throw.
Accordingly, this mode of training has been shown to elicit significant upperbody power gains (Lyttle et al. 1996). It is suggested the greater velocity and
movement pattern specificity of ballistic training is more likely to stimulate
functional high-velocity adaptations (Cronin et al. 2003) than traditional
resistance training. Accordingly, bench throw training is shown to elicit
significant improvements in functional performance in elite baseball players
(McEvoy and Newton 1998). A practical consideration with this ballistic
training mode is that it requires costly apparatus to safely restrict the barbell
to vertical-only movement and to brake the descent of the bar once it is
released. One alternative is to substitute the ballistic push-up exercise; this
circumvents the need for expensive specialised equipment to catch an external
load as the athlete’s own body mass is the load that is projected into free
space. When compared to standard modified push ups (supported on the
knees), ballistic modified push-up training (hands leaving the floor at the top
of the movement) is reported to elicit significantly greater improvement in
ballistic power, as assessed by medicine ball throw distance, and similar gains
in strength (chest press 1-RM) scores in female subjects (Vossen et al. 2000).
Mechanisms
The majority of ballistic resistance training exercises are preceded by an
eccentric action or countermovement. As such, the interaction between
muscle and tendon during these training modes differs to that seen with
concentric training modes such as Olympic weightlifting exercises.
Specifically, the majority of the shortening during the concentric portion of
the movements occurs at the tendon, with limited change observed in muscle
fascicle length (Kawakami et al. 2002). Essentially, the muscle contracts in a
quasi-isometric fashion in order to add tension to the tendon ‘spring’. The
significance of the eccentric action is evident in that the majority of the
improvement in (concentric) power output following ballistic resistance
training (jump squats) is attributed to adaptations associated with the
eccentric phase (Cormie et al. 2010b). These adaptations may include changes
in the mechanical properties of the muscle–tendon unit, as is observed
following plyometric training (Foure et al. 2010).
Intra-muscular co-ordination aspects include improved recruitment and
firing of high-threshold motor units at the high contraction velocities
associated with the ballistic training movement (Stone 1993; Hedrick 1993).
Maximal ballistic muscle actions involve appreciably higher motor unit firing
rates than those observed with conventional strength training (Behm 1995;
Hedrick 1993). Ballistic contractions appear to be part pre-programmed by
higher motor centres in anticipation of how the ballistic action is expected to
occur, with some modification of motor unit activation based upon sensory
feedback during the movement (Behm 1995). It follows that repeated exposure
will result in a learning effect, resulting in an enhanced ability for motor units
to fire rapidly during the short interval for force development allowed by the
ballistic action (Ives and Shelley 2003). In support of this, training adaptations
reported following ballistic training include an increase in peak firing
frequency, and this higher rate of firing also appears to be maintained
throughout an extended portion of the concentric movement (Cormie et al.
2011a).
Inter-muscular co-ordination and antagonist co-contraction is likewise
largely pre-programmed, and is believed to be a protective mechanism acting
to maintain joint integrity in anticipation of the forces and limb accelerations
during the ballistic action (Behm 1995). Fine-tuning of antagonist input with
repeated exposure to the ballistic training movement may occur to reduce cocontraction to increase net concentric force output. The acceleration–
deceleration profiles associated with bench throw training have been
suggested to more closely resemble sporting activities (Cronin et al. 2003).
This being the case, similar advantages in terms of improving performance via
enhanced inter-muscular co-ordination may be conferred by ballistic training.
Controversy regarding maximal power ‘Pmax’ training
approach
It has been contended that ballistic training with ‘Pmax’ loads that maximise
mechanical power output is the optimal means of developing explosive
muscular power (Wilson et al. 1993; Baker et al. 2001a, 2001b). These methods
have proven effective in developing power output and scores for dynamic
athletic performance (Wilson et al. 1993). However, from a methodological
point of view, attempts to identify players’ individual Pmax loads often
produced variable results. Values for Pmax derived by many earlier studies
appear to be affected by numerous factors including the constraints of the
training activity and the relative strength and strength-training history of
subjects tested (Baker 2001c; Harris et al. 2007).
Similarly, the practical significance of this Pmax load has been called into
question by a number of authors. In view of the multidimensional nature of
explosive muscular power developed discussed earlier in the chapter, it seems
counterintuitive that training a single percentage 1-RM load would be the
optimal way to develop speed-strength capabilities (Cronin and Sleivert 2005).
Data from elite senior team sports athletes (rugby union players) also show
that power output at different loads either side of the Pmax load value in fact
differs very little for a given training movement (machine jump squats)
(Harris et al. 2007).
Figure 6.3 Barbell bound step up
More recent studies have highlighted flaws in the methodology and
calculation methods used to derive Pmax values (Cormie et al. 2007a). For
instance, it has been identified that measured peak power differs for the
barbell versus the athlete’s own body, and peak barbell power values are
maximised at a considerably different external load (80 per cent of squat 1-RM
for the barbell jump squat) than the peak power measured for the athlete’s
body (0 per cent of squat 1-RM) (McBride et al. 2011). When calculated
correctly, the actual external load that maximises mechanical power output
for the body + barbell ‘system’ for the jump squat ballistic training exercise
has been repeatedly shown to equate to zero – i.e. body mass resistance
(Cormie et al. 2007b; Dayne et al. 2011; McBride et al. 2011).
Whatever the P max load identified, employing this training approach in
isolation tends to neglect the principles of specificity. Although a particular
training load may be optimal for developing mechanical power output for a
given movement, if the loading bears no relation to the resistances the athlete
faces during competition then the degree of transfer to performance appears
questionable. Training at a single relative load is similarly unlikely to elicit
improvements in other regions of the force–velocity curve. Employing a
variety of loads would therefore appear the best approach (Cronin and
Sleivert 2005).
The contribution of the player’s own body mass should be considered when
selecting the external load for ballistic resistance exercises such as jump squat
and ballistic push up which involve the body being projected into free space
(Cronin and Sleivert 2005). Practically, there will also tend to be a trade-off
between the degree of external loading used versus lifting form and the
explosiveness with which the player is able to execute the movement.
Qualitative assessment of posture and lifting technique as well as velocity and
height achieved should therefore also be used to guide loading when players
perform ballistic resistance exercises.
Limitations
Standard ballistic resistance training modes are often bilateral (for example,
barbell jump squat) and typically feature predominantly vertical force
production. As such these training modes develop speed-strength qualities in a
way that will transfer most readily to bilateral movements in a vertical
direction – hence the efficacy of jump squat training in improving vertical
jump measures. However, these training modes are less effective in
developing power expression during cyclic unilateral movements in a
horizontal direction – such as sprinting. A 10-week study employing jump
squats improved jump height measures, isokinetic knee extension scores and
6-second cycle performance without any significant improvement in 30m
sprint (Wilson et al. 1993).
Variations of ballistic resistance training modes performed in a split stance
or from a unilateral base of support could be employed, which could
conceivably offer greater transfer to unilateral movements. One such example
is the bound (barbell) step up exercise (Figure 6.3). Other examples include
concentric only versions of training exercises commonly used for plyometrics.
These exercises typically use only body weight resistance, but potentially
added resistance in the form of a barbell or dumbbells could be applied. To
date, very little attention has been given to such exercises in the literature –
further study would be required in order to establish if these training modes
might be effective and identify what degree of external resistance would be
appropriate.
Figure 6.4 Alternate leg split bounds
Plyometric training
Applications
Plyometrics are a special class of speed-strength training exercises that
emphasise the coupling of eccentric and concentric actions and the
development of SSC capabilities (Matavulj et al. 2001). There are essentially
two categories of plyometric training modes. Slow SSC plyometric exercises
are characterised by a preparatory eccentric phase but are performed from a
fixed base of support, for example, the countermovement jump. Fast SSC
plyometric training modes essentially feature a preceding flight phase, so that
the duration of ground contact is very brief. One example is the drop jump
exercise; however, fast SSC plyometrics also include repeated jump
movements and cyclic bounding activities.
The major benefit associated with plyometric training is developing the
athlete’s capacity to harness SSC augmentation of concentric power output.
For example, athletes who participate in sports such as long jump and triple
jump which have a significant SSC component exhibit increased lower limb
active musculo-tendinous stiffness when performing SSC tasks such as
hopping (Rabita et al. 2008). Accordingly, the addition of plyometric training
to the physical preparation of trained elite junior athletes is shown to elicit
significant improvements in vertical jump performance in these athletes
(Matavulj et al. 2001). A meta-analysis of the research literature has reported
that both slow SSC (countermovement jump) and fast SSC (drop jump)
plyometric training modes produce significant improvement in vertical jump
performance (Markovic 2007).
A similar review of the literature on the effects of plyometric training
interventions on sprinting performance also reported favourable results (Saez
de Villarreal et al. 2012). This is a particularly significant finding as other
speed-strength training modes often exhibit very limited transfer to measures
of running speed. This study also identified factors relating to the design of
the plyometric interventions that were associated with superior training
outcomes with respect to sprint performance. For example, employing
different modes of plyometric training in combination, and the inclusion of
plyometric exercises that feature horizontal propulsion, appears to maximise
gains in speed performance (Saez de Villarreal et al. 2012). From a specificity
viewpoint, cyclic unilateral horizontal bounding and jumping plyometric
exercises (in a horizontal direction) would appear the most appropriate
training modes to develop sprint capabilities (Young 2006). Bounding in
particular features comparable horizontal propulsion forces, foot contact
position and contact times, and muscle activation to those recorded during
sprinting (Mero and Komi 1994). Accordingly, an early study that employed
plyometric training which included unilateral jumping and bounding
exercises in a horizontal direction reported improvements in acceleration (10m
sprint time) and overall 100m sprint scores (Delecluse et al. 1995).
It has similarly been identified that the kinematics of the eccentric phase
differ markedly for a variety of unilateral countermovement jump movements
performed in different directions (Meylan et al. 2010). Peak velocity achieved
during the eccentric phase showed a positive statistical relationship to
horizontal jump distance for both forwards and lateral variations of the
unilateral horizontal countermovement jump in this study, whereas no such
relationship was seen for jump height achieved in the unilateral vertical
countermovement jump test. The necessity for both slow and fast SSC
plyometric exercises to reflect the multidirectional activities performed in the
sport therefore not only concerns developing horizontal propulsion in the
relevant directions, but also exposing the player to the specific eccentric
actions involved in these movements in order to confer the specific
neuromuscular adaptations required.
Mechanisms
The SSC training stimulus provided by plyometric training has shown to elicit
improvements in shortening velocity and peak power output of single type II
muscle fibres (Malisoux et al. 2006). Plyometric training is also associated with
structural adaptations to tendon structures (Fouré et al. 2010). Although
tendon cross-sectional area appears unchanged following a short-term
plyometric intervention, qualitative changes in tendon structure have been
observed. These adaptations alter the mechanical properties of the tendon,
including changes to both stiffness and energy dissipation (Fouré et al. 2010).
In addition to such mechanical adaptations to contractile and connective
tissues, the mechanisms for the improved SSC performance with repeated
exposure to plyometric training are also of neural origin. Alterations in intramuscular co-ordination include changes to descending neural input from
higher motor control centres. One aspect of the neural activation response to
plyometric exercise is the pre-activation of agonist muscles during
preparatory and eccentric phases of both slow SSC (for example,
countermovement jump) and fast SSC (for example, drop jump) movements
(McBride et al. 2008). This pre-activation of agonist muscles increases the
active stiffness of the muscle–tendon complex. Specifically, activating the
muscle in the interval before touchdown means that the tendon is placed
under tension prior to ground contact. An associated effect of this is that there
is minimal change in muscle fascicle length during ground contact so that the
majority of the change in length occurs at the tendon, which is further
stretched during the eccentric phase and then rapidly shortens due to elastic
recoil during the concentric phase prior to take-off. This serves to enhance the
storage and return of elastic energy during eccentric and concentric phases,
respectively.
Another postulated effect of this descending input is to modulate locally
mediated inhibition of stretch reflex neural pathways (via Golgi tendon organ)
immediately prior to and during the pre-stretch phase (Taube et al. 2008).
Plyometric training is thus suggested to result in ‘disinhibition’ of stretch
reflex-mediated neural drive during the countermovement, which acts to
augment power output in the subsequent concentric phase (Newton and
Kraemer 1994).
The described adaptations elicited by lower-body plyometric exercises are
manifested in enhanced concentric power and rate of force development
(RFD) of the lower limb extensor muscles (Matavulj et al. 2001). Plyometric
training in the form of depth jumps is reported to elicit improvements in
eccentric RFD with short-term progressive training at increasing drop heights
(Wilson et al. 1996). This improvement in rate of eccentric force production is
suggested to enhance storage of elastic energy in the musculo-tendinous unit,
which underpins observed improvements in SSC performance in response to
progressive plyometric training (Wilson et al. 1996).
Limitations
Despite the extensive use of plyometric training in particular for lower-body
dominated athletic training, there is a lack of systematic investigation to
determine the optimal load for plyometric exercises (Wilson et al. 1993).
Standard methods for upper- and lower-body plyometric training are likewise
yet to be established empirically (Vossen et al. 2000). In the absence of such
data, body weight is typically used as resistance due to convenience; this
factor may contribute to the lesser improvements in power output during
concentric movements compared to other speed-strength training modes
(Wilson et al. 1993). However, it may conversely be that it is
counterproductive to add loading to plyometric movements on the basis that
this may lead to a protective inhibitory effect upon neural activation – as has
been noted with depth jumps when added load is applied. In support of this
contention, a meta-analysis of studies relating to plyometric training and
sprint performance reported that the addition of external resistance produced
no further benefit (Saez de Villarreal et al. 2012).
Decisions regarding exercise selection and progression when designing
plyometric training interventions are complicated by uncertainty regarding
the efficacy of published guidelines pertaining to the relative intensity of
various plyometric training modes. Recent investigations have reported that
muscle activity (EMG) and ground reaction forces measured during a variety
of plyometric exercises in some cases bear little resemblance to intensity
guidelines published for these exercises (Ebben et al. 2008, Wallace et al. 2010).
Similarly, volume guidelines are often based upon arbitrary limits for the
number of ‘foot contacts’ during a session. In contrast a recent meta-analysis
noted greater effects on sprint performance when volume per session
exceeded 80 jumps (Saez de Villarreal et al. 2012).
Whether the augmented neural activation to agonist muscles during
plyometric exercise translates into increased jump height or distance depends
on the net balance between the augmented concentric energy production
versus the amount of energy absorbed during the eccentric phase (McBride et
al. 2008). For example, drop jump height may or may not be greater than
countermovement jump height, depending on the reactive speed-strength and
fast SSC capabilities of the player. A player’s performance when undertaking
high-intensity plyometric training will therefore depend upon their training
history, including maximum strength capabilities and also prior exposure to
eccentric loading and SSC movements. Plotting players’ jump height for squat
jump, countermovement jump, and drop jumps executed from a range of drop
heights offers a means to profile their SSC abilities. Above a certain ideal drop
height for the player there is a withdrawal of neural pre-activation, which is
reflected in a steep decline in jump height achieved when this critical drop
height is exceeded. This appears to be a protective response which is
modifiable with training.
Drop jumps would appear to be a poor choice for improving sprinting
speed, given that they are typically performed bilaterally and feature force
production in a vertical direction (Young 2006). Accordingly, a 10-week
training period using drop jumps produced no significant gains in 30m sprint
scores despite significant improvements in countermovement jump (Wilson et
al. 1993). Similarly, the interval for force production during sprinting (dictated
by foot contact time) is less than half that for vertical jumping, and much
shorter than that allowed by speed-strength training modes (Mero and Komi
1994). This may be a factor in the frequent failure of speed-strength training
studies to produce significant effects in sprint performance over longer
distances (30–40m), despite concurrent improvements in vertical power
measures and acceleration (10m sprint) parameters (Wilson et al. 1993; Lyttle
et al. 1996; Harris et al. 2000).
It has been noted previously that specific upper-body power training is
underprescribed by strength coaches (Baker and Nance 1999a). The majority
of plyometric exercises featured in training and research are typically lowerbody intensive (McEvoy and Newton 1998), with training to develop SSC
capabilities in upper-body movements receiving little attention in the
literature (Newton et al. 1997). The few upper-body-targeted plyometric
exercises that are implemented typically employ weighted medicine balls to
provide resistance. The training stimulus provided by such weighted
implements represents a far smaller external loading compared to the
corresponding lower-body plyometric exercises. Practically, to project a
medicine ball or other weighted implement heavy enough to provide the
requisite external loading (46–63 per cent 1-RM) from a supine position is not
feasible without the use of specialised equipment. Accordingly, drop medicine
ball throws failed to produce the enhancement in rate of eccentric force
development conferred by lower-body plyometric depth jump training
(Wilson et al. 1996).
Variations of a ballistic push up show potential use as equivalent upperbody plyometric training modes. For example, a ballistic push up executed
with countermovement might be used to develop slow SSC capabilities,
whereas a drop ballistic push up initiated from raised blocks could serve as
fast SSC plyometric training. The latter training mode is equivalent to the
plyometric push up test described in the study by Jones and colleagues (1999).
Complex training
Applications
Complex training, or contrast loading, is a method often used in conjunction
with ballistic or plyometric exercises. Contrast loading incorporates a heavier
load strength-oriented exercise prior to performing a full acceleration
(typically ballistic) exercise (Young et al. 1998; Baker 2003). This approach
attempts to harness transient mechanical and neural effects of the preceding
heavy load to augment power output when the speed-strength exercise is
subsequently performed (Baker 2003). This phenomenon is termed postactivation potentiation (Chiu et al. 2003).
Essentially, a preceding muscle contraction has two residual effects which
affect twitch contraction force in the interval that follows. One effect is
fatigue; the other is post-activation potentiation (Kilduff et al. 2007). It is the
net effect of these two opposing effects that determine the acute performance
response at a given time point following the initial activity. Attempts to
manipulate these transient effects therefore aim to minimise fatigue whilst
harnessing potentiation effects (Kilduff et al. 2007).
The key aspects of optimising performance enhancement and minimising
detrimental fatigue effects are the load and volume used with the preceding
primer set and the rest interval employed between primer set and the target
activity (Kilduff et al. 2007). Both isometric (Paasuke et al. 2007) and dynamic
heavy resistance modes have been successfully employed to produce postactivation potentiation effects – typically studies have used the back squat
exercise with near maximal resistance (Chiu et al. 2003). However, short-term
performance enhancement has also been reported with an intervening set at a
heavier resistance with the same ballistic exercise (jump squats) (Baker 2001d).
Theoretically employing a speed-strength exercise as the preload set should be
beneficial from the point of view of minimising residual fatigue effects.
Studies examining rest intervals have typically employed heavy load barbell
squat and bench press as the preceding resistance exercises for lower-body
and upper-body movement respectively. It has been reported that recovery
time in the range of 8–12 minutes appears optimal for observing performance
enhancement (Kilduff et al. 2007). However, this may vary according to both
the contraction mode featured in the preload set and the training history of
the individual player (Paasuke et al. 2007).
Mechanisms
Tension-sensitive contractile and neural mechanisms have been identified as
underlying the acute performance effects observed with contrast loading
(Baker 2003, Chiu et al. 2003). Mechanical factors are suggested to involve
transient changes in stiffness of series elastic components within the musculotendinous unit. One of the biochemical changes identified as underlying such
contractile effects is phosphorylation of regulatory myosin light chains
initiated by calcium release during the initial muscle action (Chiu et al. 2003).
This process renders the actin–myosin complex more sensitive to further
calcium release during subsequent muscle contraction – hence its proposed
role in post-activation potentiation (Paasuke et al. 2007).
The various postulated neural mechanisms principally involve acute
changes in autogenic regulatory inputs to motor units involved in the
movement (Kilduff et al. 2007). Part of the modification of peripheral
pathways involved is likely to originate from descending input from higher
motor centres. The probable mediating factors at the level of the motor unit
are the Golgi tendon organ (GTO) and Renshaw cell. The net peripheral
effects are suggested to comprise reduced inhibitory input to the agonist
muscles and increased reciprocal inhibition of antagonist motor units (Baker
2003). These mechanical and neural effects are transient and are reported to
dissipate approximately 20 minutes after performing the initial high-intensity
preload set (Kilduff et al. 2007).
Limitations
Due to the paucity of data regarding contrast loading, chronic effects
associated with the use of complex training have to date received little
research attention (Paasuke et al. 2007). As a result, possible mechanisms for
any performance improvement elicited by the long-term use of complex
training are yet to be determined. The application of these methods also
appears dependent upon the training status of the individual. Significant
positive correlation is reported between lower-body strength and the degree of
potentiation, which suggests that the mechanisms underlying acute
performance augmentation play an increasing role with advances in training
status (Young et al. 1998). In accordance with this, it was reported that
performance enhancement consistent with post-activation potentiation was
observed in athlete subjects whereas the recreationally trained subjects
studied did not show such a response (Chiu et al. 2003). Another study
identified that power athletes appear to exhibit differing responses to
endurance athletes with respect to post-activation potentiation (Paasuke et al.
2007). Both the magnitude and the time course of post-activation potentiation
may therefore differ according to players’ training background.
To date, acute contrast loading effects have been most widely documented
with lower-body exercises, typically with jump squats as the target ballistic
activity. Acute potentiation of dynamic lower-body performance has been
observed with standing long jump, vertical jump and jump squat scores when
performed immediately following a heavy load set with a strength-oriented
lower-body exercise (Young et al. 1998; Baker 2003). Data for upper-body
complex training has been more equivocal. It has recently been elucidated that
a lesser load (≈65 per cent bench press 1-RM) for the primer exercise set
appears to be more effective in producing enhanced power output in the
subsequent target upper body power activity (Baker 2003). This was identified
as the reason why previous studies featuring heavier upper-body contrast
loads (85–90 per cent bench press 1-RM) did not observe any acute
performance augmentation effect (Baker 2003). However, a recent study
featuring professional rugby union players did report significant, albeit
modest, increases in peak power output for ballistic bench throws at different
time points following a bench press 3-RM ‘preload’ set (Kilduff et al. 2007).
Co-ordination training
Applications
In the case of fine motor skills, the training stimulus must feature a high
degree of specificity with respect to the movement patterns and velocity
encountered in competition in order for improvements in power output to
transfer to the particular sports skill movement (Kraemer et al. 2002). This is
likely to be particularly evident with experienced athletes (Newton and
Kraemer 1994). Key factors are intra-muscular and inter-muscular coordination, and in particular the degree and timing of agonist, synergist and
antagonist muscle activation. The concept of co-ordination training has been
introduced to describe training modes that satisfy these criteria (Newton and
Kraemer 1994).
The term ‘co-ordination training’ thus describes training modes that feature
co-ordination of agonist, synergist and antagonist muscle groups in a way that
closely replicates the movement patterns and velocity of an athletic activity
(Newton and Kraemer 1994). Many sports skill activities, such as throwing
and striking movements, involve motion in the transverse plane and
generation of rotational torques and transfer of angular momentum
throughout the kinetic chain via sequential motion of multiple segments
(Aguinaldo et al. 2007). Conversely, the different training modes described in
the previous sections predominantly involve linear acceleration movements.
Accordingly, successful co-ordination training modes typically apply
resistance directly to the specific skill movement (Escamilla et al. 2000; van
den Tillar 2004). For example, pulley devices have been used for developing
power for the overarm throwing movement (Ettema et al. 2008).
A number of studies have investigated co-ordination training interventions
to develop power output for the (one-handed) overhead throwing movement.
The rationale behind the use of weighted implements when carrying out
ballistic sports skills is that resistance is provided during the actual target
movement. It therefore follows that the training implement employed for
ballistic resistance training should be of the same dimensions as that used in
the particular sport. A variety of underweight and overweight balls have been
employed as a means to provide overload in the form of velocity and force,
respectively (van den Tillar 2004). The benefits of underweight ball training
interventions have been reported previously by a number of studies
examining overarm throwing sports (van den Tillar 2004). Likewise,
combination training, featuring both overweight and underweight balls, has
reported to be successful in improving overarm throwing velocity with
regulation balls (DeRenne et al. 1994, 1990). However, results of studies
featuring overweight ball training interventions in overarm throwing sports
players have been more variable (Escamilla et al. 2000; van den Tillar 2004).
Crucially, throwing accuracy also appears to be maintained at the enhanced
throwing velocities post-training (Escamilla et al. 2000).
Previously, the data of DeRenne et al. (1994) indicated that a load variation
of ±20 per cent regulation weight was successful for under- and over-weight
training interventions, which is consistent with previous data for athletic
throwing events (Escamilla et al. 2000). Other overarm throwing studies have
reported success with balls that are 100 per cent overweight (van den Tillar
2004). The overarm warm-up study by van Huss et al. (Van Huss et al. 1962),
that successfully showed acute enhancement of throwing velocity, employed
11oz balls, which were 120 per cent heavier than regulation ball weight.
However, overarm training studies employing overweight balls of this degree
of difference (>100 per cent regulation weight) have typically not reported
improvements in throwing velocity (van den Tillar 2004).
A more recent study has investigated co-ordination training on the twohanded overhead throwing movement performed in team sports such as
soccer, basketball and netball (van den Tillar and Marques 2011). It was
suggested that the loading employed with the weighted ball training
intervention is likely to be a critical factor. In this investigation, significant
increases in overhead throwing velocity were reported following a 6-week
training period with a 3kg medicine ball; this is over six times heavier than a
regulation soccer ball (van den Tillar and Marques 2011). A similar finding
was noted in an investigation of weighted ball training intervention for the
two-handed spin pass with a rugby ball (Gamble 2005). These findings suggest
that the magnitude of loading for two-handed throwing movements in team
sports may exceed what has been reported to be optimal for one-handed
overarm throwing.
Mechanisms
The precise mechanisms for increases in throwing velocity with modified
(heavy and light) ball training are yet to be elucidated. The increases in
velocity for the passing skill observed in the current study are likely to be
mediated by neural factors, on the basis that the relative loading offered by
the heavy ball is probably insufficient to elicit morphological changes. These
underlying neural factors likely include improvements in rate of force
development (RFD). This RFD parameter is dependent on the rate at which the
musculature is activated (Stone et al. 2003b), and increases can be attributed
primarily to enhanced motor firing in the brief time interval for force
production allowed by the sports skill (Behm 1995). Gains in high-velocity
strength in the specific musculature involved in the passing movement may
also have been a factor. Authors of a previous overarm throwing study
hypothesised that improvements in the ability to selectively recruit highthreshold motor units may play a role (DeRenne et al. 1994). It is likewise
possible that improved inter-muscular co-ordination of agonist, synergist and
antagonist muscle firing may also contribute to gains in throwing velocity.
Limitations
A very high degree of specificity of loading does appear to be necessary in
order for speed strength modes to transfer to sports skill performance. This is
perhaps unsurprising given the very high degree of co-ordination in the
magnitude and timing of sequential motion between multiple segments in
series that feature in skilled movements such as throwing (Aguinaldo et al.
2007). For example, the divergence in motor patterns involved with twohanded overhead and chest pass medicine ball throws are apparently too great
to stimulate a training effect for baseball throwing velocity, even in junior
players with no resistance training experience (Newton and McEvoy 1994).
Similarly, despite the greater similarity noted for the force–time curve for the
bench throw movement, bench throw training was not found to offer any
advantage to conventional bench press training in developing netball pass
velocity in female players (Cronin et al. 2001b). The authors concluded that
the movement velocity involved in the bench throw was too dissimilar to the
netball chest pass movement to evoke superior gains in chest pass velocity in
relation to conventional bench press training.
In the case of fine motor skills, it has been proposed that if the contrast in
load is too great then disruption of the precise motor patterns of the sports
skill would occur, thereby nullifying any benefits of training (Baker 2001d).
Skilled movements such as one-handed overarm throw are reliant upon
precise control of the degree and sequential timing of rotational motion of a
series of segments in order to translate angular momentum from the hips to
the throwing arm (Aguinaldo et al. 2007). In this case, if the overweight ball
was too heavy, the player will have to adjust their throwing mechanics to
compensate, at the risk of causing disruption to this highly co-ordinated
sequential motion. For example, in the one-handed overarm throwing study
by Straub (1968), subjects threw balls that were progressively increased in
weight each week, culminating with 17oz balls (240 per cent heavier than
regulation) in the final week of the study, and no improvement in throwing
velocity with the regulation ball was derived.
It is also noteworthy that increases in performance reported by coordination training interventions that employ weighted implements are often
no different from the improvements elicited by performing repetitions without
any added load. For example, in the two-handed overhead throwing study, the
improvement in throwing velocity following the 6-week training period did
not differ for subjects in the group who trained only with a standard ball, in
comparison to the medicine ball training group or combination (medicine ball
and standard ball) training group (van den Tillar and Marques 2011). Similar
findings have been noted previously in a study of sprint training methods,
which reported that a training group performing only standard sprint training
showed superior improvements to groups that employed either resisted
sprinting or assisted sprinting training interventions (Kristensen et al. 2006).
Co-ordination training modes that employ heavier or lighter sports skill
implements appear most appropriate for ballistic sports skills – such as
throwing – where the implement can be released at the end of the movement.
It is more problematic to employ this form of training with other sports that
involve an implement such as a racquet or a bat which is held throughout. For
example, if swinging a heavier version of a racquet, at the termination of the
swing the momentum of the heavier implement has to be absorbed by the
limbs and joints. This carries obvious risks of injury, particularly if performed
repetitively. For these striking sports, resistance in the form of a cable pulley
system may offer a safer and more viable alternative for co-ordination
training. In particular, cable machines with pneumatic resistance may provide
a means to allow ballistic-type striking movements to be performed with
lighter loads without the issues of causing damage to the apparatus that can
occur with weight stack loaded cable machines. However, studies to date have
only investigated the use of pulley devices to develop throwing velocity; there
are currently no data to validate the application of this approach for striking
movements.
Conclusions and training recommendations
Power is clearly multidimensional, and developing this capacity is dependent
upon a range of morphological, mechanical and neuromuscular adaptations
(Cormie et al. 2011a). It follows that achieving optimal development of power
will require a variety of training approaches in order to account for each of
the different factors that contribute to the ability to express explosive
muscular power. The selection of training modes will depend upon the
athletic or sports skill movement in question (Baker and Newton 2005). The
optimal approach will to some extent also depend upon the profile and
training history of the individual player. The degree to which a particular
mode of training is effective in developing explosive power capabilities will be
influenced by the amount of adaptation that has already taken place in the
corresponding factor underpinning power expression.
For example, a key consideration is the strength base of the individual and
their window for adaptation (Baker and Newton 2005). In the case of players
with low to moderate strength-training experience, and corresponding
maximum strength levels, appropriate strength training is likely to confer
improvements in both strength and power (Cronin et al. 2001b; Newton and
McEvoy 1994). For those with a greater strength-training base, diminishing
returns are observed so that only modest improvements in power will be
observed despite gains in strength. The emphasis for these players must
therefore shift to greater use of specific speed-strength training modes in order
to produce any significant increase in power (Cormie et al. 2011b).
In general, employing a combination of speed-strength training modes
during the course of the training macrocycle is likely to offer superior
improvements in power over time (Cormie et al. 2011b). Olympic
weightlifting training modes confer improvements in concentric power
development and maximise power expression against greater external
resistance. Ballistic resistance training offers a means to elicit gains in
concentric power output due in part to improvements in the eccentric phase;
peak power measured for both the athlete’s body and body + mass ‘system’
during the barbell jump squat are also significantly higher than values
achieved during the power clean at a range of barbell loads from 0–80 per cent
of squat 1-RM (McBride et al. 2011). Plyometric training provides
improvements in both slow SSC and fast SSC properties, and a high degree of
movement specificity is possible with plyometrics, which favours transfer to
horizontal propulsion and multidirectional movement. Finally, co-ordination
training modes represent a means to develop specific power capabilities for
sports skills, such as throwing and striking movements.
Planned variation has been identified as an important factor in optimising
gains in explosive power performance over time (Winchester et al. 2008). This
pertains to both the training modes employed and intensity prescribed for
speed-strength training. Superior gains in power are generally achieved when
a range of loads are employed in the course of a training intervention (Cormie
et al. 2011b). An undulating periodisation format, featuring alterations in
training intensity both between workouts and successive training weeks, has
been employed successfully in short-term (8 week) speed-strength training
studies (Winchester et al. 2008).
The session format will also have a bearing on the training stimulus and
force and velocity parameters during successive sets and repetitions. The
amount of rest employed between sets when performing Olympic
weightlifting training (three sets of six repetitions of the power clean with 80
per cent 1-RM resistance) was reported to significantly influence the
decrement in peak power, force and velocity measures in sets two and three
(Hardee et al. 2012). Similarly, the format of each set can be manipulated
when performing speed-strength training to provide variation and enhance
the quality of each repetition (Haff et al. 2008). One such approach involves
the use of ‘cluster’ or ‘rest-pause’ sets: this format incorporates a brief rest
period between individual repetitions within the set. Lifting velocity was
reported to be better maintained for consecutive repetitions of an Olympic
weightlifting exercise (barbell clean pull) when sets were performed in a
cluster set format (Haff et al. 2003). Similar findings were observed with
respect to power output and velocity when repetitions of a ballistic resistance
exercise (barbell jump squat) were performed in clusters of one, two or three
repetitions with rest intervals between, in comparison to the traditional
format of performing six repetitions consecutively (Hansen et al. 2011). These
findings are particularly noteworthy as the latter study employed professional
and semiprofessional team sports players with extensive training experience.
Implementing this approach is therefore suggested to optimise the mechanical
stimulus provided (Hansen et al. 2011), and is likewise beneficial in terms of
neural co-ordination aspects (Haff et al. 2008). Varying the set format at
different times in the training cycle according to the goals of the training
phase (for example, power versus power-endurance) is another tool strength
and conditioning specialists may use when periodising players’ speed-strength
training.
7
SPORTS SPEED AND AGILITY DEVELOPMENT
Introduction
It is acknowledged that speed and agility in team sports represent complex
psychomotor skills (Verkhoshansky 1996). Training to develop speed and
agility would therefore appear to demand a high degree of neuromuscular
specificity. There are likewise issues of biomechanical specificity that must be
considered when designing speed and agility training for a particular team
sport. Perceptual components that underpin sports speed and agility must also
be accounted for when developing these qualities, which include anticipation
and decision-making; these constraints will be specific to the sport and
playing position.
Developing speed capabilities necessarily comprises a variety of elements.
For example, strength qualities are implicated in the need for the athlete to
overcome their own inertia, such as during initial acceleration. Speed-strength
and stretch-shortening cycle abilities are likewise required every time the foot
touches down to propel the body forwards. In addition to physical capabilities,
speed expression is highly dependent upon neuromuscular co-ordination and
technique aspects. All of these components must be trained in a way that is
specific to the form of locomotion (such as running or skating), and
movement velocities that feature in the sport, in order to ultimately transfer to
sports performance.
Change of direction performance is relatively independent of straight-line
speed performance (Little and Williams 2005; Young et al. 2001a). The
multidirectional acceleration and deceleration involved in change of direction
movements, which in turn underpin agility performance, are therefore specific
qualities and should be trained as such (Jeffreys 2006). Team sports agility
comprises not only these change of direction abilities, but also the capability
to anticipate, read and react to game-specific cues in the environment
(Sheppard and Young 2006; Young and Farrow 2006).
Due to the variable nature of match-play, high-velocity movements may be
initiated from a variety of starting conditions. Similarly, exhibition of both
speed and agility in team sports occurs in response to game situations (Young
et al. 2001a). It follows that perception–action coupling and decision-making
are critical elements in terms of developing the ability to express speed and
agility capabilities under match conditions.
Trainability of speed and agility capabilities
Traditionally there has been some debate among coaches about whether speed
capabilities are trainable. To some extent there has been a shift in opinion
over recent years and coaches increasingly acknowledge that while genetic
aspects do exert major influence there is growing acceptance that an athlete’s
speed capabilities can be developed via appropriate training interventions. In
the case of agility development this debate is to some extent ongoing (Gamble
2011a).
There is an increasing body of data that support the efficacy of training
interventions to develop both change of direction abilities (Brughelli et al.
2008) and the perceptual and decision-making aspects of agility (Serpell et al.
2011). It is also clear that dedicated training will be required in order to elicit
such improvements; speed training alone will not be reflected in improved
change of direction performance (Young et al. 2001a), or in turn agility
expression in the sport.
Specificity of speed versus agility development
Players’ straight-line sprinting scores and measures of change of direction
performance that are indicative of agility typically show only limited
statistical relationship. In a study of professional soccer players’ scores on
acceleration, maximum speed and change of direction tests showed low
coefficients of determination (Little and Williams 2005). The authors
concluded that speed and agility are distinct abilities that are relatively
independent of each other. Furthermore, correlations between measures of
these abilities reportedly decrease markedly when any sport skill component
is incorporated in the agility tests (Young et al. 2001a).
These findings reflect the dissimilarity of movement mechanics between
straight-line running and the locomotion employed during change of direction
tasks (Sheppard and Young 2006; Young et al. 2001a). Major differences
include stride mechanics and the requirement for deceleration and lateral
acceleration, and the fact that change of direction movements involve
considerable hip abduction and generation of medial–lateral ground reaction
forces (McLean et al. 2004).
The specificity of training effects is reinforced by the very limited transfer
to change of direction performance reported following a six-week period of
straight-line sprint training (Young et al. 2001a). In this study, as the
complexity of the agility test increased (greater number of changes in
direction and more acute angles of cutting), the degree of improvement
following the straight-line sprint training became less. The converse also
appears to be true of agility training. Following six weeks’ agility training,
performance was improved in a selection of tests with varying numbers of
changes in direction – however, no improvement was seen on a straight-line
test (Young et al. 2001a). Again, the greatest carry-over was observed on the
tests with similar change of direction complexity and angles of cutting to that
featured in the agility training employed (Young et al. 2001a). As these change
of direction abilities which underpin agility performance would appear to be
independent of straight-line sprinting ability, it follows that they must be
developed via specific training (Jeffreys 2006).
Mechanics of sprint running
Foot strike during sprinting
The duration of ground contact when sprinting is very brief and represents
the interval during which the athlete has the opportunity to propel themselves
forwards (Weyand et al. 2010). For these reasons various aspects relating to
the foot strike exert considerable influence, in terms of maximising propulsion
and minimising braking forces (Gamble 2011b). One example is the placement
of the foot with respect to the athlete’s centre of mass at initial contact. When
the athlete is in motion, it is critical that the foot is not placed so far in front
of the body that excessive braking forces result. During high-speed running
the optimal position for initial foot strike is just in front of the centre of mass
in order to maximise the effective interval of ground contact (Nummela et al.
2007).
Similarly, the orientation of the foot and lower limb, and the relative
motion of the foot when it connects with the ground, will also determine
relative braking versus propulsion forces. If the foot is moving forwards at
initial contact braking forces will result; the aim therefore is that the foot is
moving in a rearwards direction so that braking forces are minimised and
propulsion maximised (Nummela et al. 2007). The region of the foot that
makes contact with the ground is also a key factor. If the athlete strikes the
ground with their heel a dual spike of ground reaction forces results; this not
only increases impact forces but also increases braking forces (Divert et al.
2005). Better sprinters are therefore observed to make initial contact with the
ground with their midfoot or forefoot (Lieberman et al. 2010). In addition to
reducing braking and impact forces, this foot strike strategy also allows for
improved elastic storage and return of elastic energy (Jungers 2010).
The importance of arm action to stride mechanics
Although not widely identified in the literature, expert sprint coaches
frequently cite the importance of arm action to sound sprinting mechanics.
During initial acceleration athletes employ a combination of a rapid arm drive
in a rearward direction with the ipsilateral (same side) upper limb to the
forwards moving leg, and a powerful upwards and forwards arm drive with
the contralateral (opposite side) upper limb. The ipsilateral arm drive is a
feature of all phases of the sprint; essentially the counter-rotation of the
shoulders and arm drive in a rearwards direction facilitates hip rotation and
leg drive in a forwards direction. The importance of arm action to running
mechanics is illustrated when arm movement is forcibly restricted (Fujii et al.
2010). Under these constraints athletes must employ much shorter strides, for
which they attempt to compensate by increasing stride frequency.
The forwards and upwards contralateral arm swing serves a specific role
during the acceleration phase. This action is analogous to the arm swing (in a
forwards direction) that athletes perform during the propulsion phase of the
vertical jump. During the jumping action this helps to stiffen the trunk region
as the lower limb extensors propel the athlete upwards, as well as helping to
generate momentum in an upwards direction, ultimately increasing torque
generation and allowing greater jump height to be attained (Feltner et al.
1999). During the initial acceleration phase, the forwards arm drive can be
seen to serve much the same function (that is, stiffening the torso and
augmenting torque generation) for the supporting lower limb that is
extending to propel the athlete forwards as the opposite leg is being swung
forwards for the first stride.
Team sports players must also accommodate the ball or implement of the
sport (for example, hockey stick) when running. Holding or dribbling the ball
will require the player to adapt their posture and running technique, and
places constraints on arm action when running. These technique
modifications represent a specific ability that differentiates elite players from
those at lower levels. For example, skilled basketball players are observed to
increase shoulder rotation when dribbling the ball in order to maintain
normal hip and lower limb mechanics (Fujii et al. 2010). It follows that these
running technique modifications should be accounted for during speed and
agility development.
Running mechanics for different phases of sprint
running
The gait cycle when sprinting can be divided into two distinct parts:
• the contact or stance phase, which begins at initial foot strike and ends
when the foot leaves the ground – that is, ‘toe-off’ – the stance phase can be
subdivided into a braking or ‘weight-acceptance’ phase, and a propulsion
phase;
• the flight or swing phase, consisting of the initial recovery during which the
initial rearward motion of the lower limb is first slowed then reversed as the
leg is brought forwards to pass under the athlete’s centre of mass and then
swung forwards before positioning of the foot and lower limb for the next
foot strike.
There are marked differences between running mechanics during the initial
acceleration phase versus running at maximal speed. One difference is the
respective duration of the stance and swing phases. During initial acceleration
the period of ground contact is much longer; the duration of foot contacts
when running at maximal speed is necessarily very brief. Other key
differences include posture and the positioning of initial foot strike.
Specifically, during acceleration there is a pronounced forwards lean, whereas
at top speed athletes adopt an upright stance (Weyand et al. 2010). The
position of initial contact during foot strike is to the rear of the athlete’s centre
of mass during the acceleration phase in order to maximise forwards
propulsion (Kugler and Janshen 2010); at maximum speed foot strike is
marginally in front of the athlete’s centre of mass.
Expression of speed in sports
Sprinting technique of team sports players appears to differ from that of track
athletes (Young et al. 1995). It is also suggested that the acceleration phase for
team sports athletes may be shorter so that they acquire top speed within a
shorter distance in relation to track sprinters (Baker and Nance 1999). Studies
of both track and field athletes and team sports players report that measures
of acceleration performance are not closely correlated to maximum sprinting
speed (Young et al. 1995; Cronin and Hansen 2005). This is a reflection of the
fact that these abilities involve different patterns of muscle recruitment and
motor firing.
In the context of some team sports, acceleration and short-distance speed
may be of more relevance than top speed attained over longer distances
(Cronin and Hansen 2005). The distances covered at high-velocity locomotion
are typically short and this generally coincides with direct involvement in
attacking or defensive play. Team sports played on a restricted playing area
(basketball, volleyball) and some playing positions within other field team
sports will rarely engage in high-velocity locomotion over distances sufficient
to attain maximum speed (McInnes et al. 1995). Hence, training for maximum
speed would appear to be a secondary priority for these players given that
they will rarely express these capabilities on the field of play (Young et al.
2001a). Conversely, the larger playing field in team sports (rugby, soccer)
combined with the fact that players may already be in motion when they start
sprinting can allow certain playing positions to attain near maximal speeds in
some instances (Little and Williams 2005). For these players developing
maximal speed capabilities over longer distances remains a key training goal.
Aspects of agility expression in team sports
A categorical definition of agility has recently been offered: ‘rapid whole-body
movement with change of velocity or direction in response to a stimulus’
(Sheppard and Young 2006). In the context of team sports, agility therefore
comprises not only change of direction movement capabilities but also
perception and decision-making.
Change of direction movement mechanics
Much the same mechanical principles as those described for straight-line
running govern propulsion during the acceleration phase of change of
direction movements (Gamble 2011c). For example, body lean angle in the
intended direction of movement and the positioning of the foot relative to the
athlete’s centre of mass will serve to determine the vertical and horizontal
component of ground reaction forces; and hence the net propulsion in a
horizontal direction (Kugler and Janshen 2010). However, by definition change
of direction movement requires generation of medial-lateral ground reaction
forces that are not evident during straight-line running (McLean et al. 2004).
As a result there are corresponding differences in muscle recruitment, in
particular there is greater adductor and abductor muscle involvement, and
there is a direct contribution from different muscles of the hip girdle to
producing movement.
Depending on the athlete’s initial velocity and degree of deviation from
their original path, change of direction movements will often comprise a
‘weight-acceptance’ phase during which the athlete must decelerate their
momentum, closely followed by a propulsion phase to move in the new
direction (Brughelli et al. 2008). The deceleration component of such change of
direction activities requires generation of braking forces. These deceleration
movements demand postural adjustments, in order to reposition the player’s
centre of mass and help slow their momentum, and considerably different foot
placement and ground contact from that described for straight-line running.
Deceleration movements are therefore described as a specific ability (Griffiths
2005; Lakomy and Haydon 2004). Furthermore, the transition between
deceleration and acceleration phases during change of direction activities
comprises additional aspects associated with the coupling of eccentric and
concentric actions (Gamble 2011c).
Sensorimotor, perceptual and decision-making aspects
of agility
Change of direction movements impose greater demands in terms of balance
abilities, particularly dynamic stabilisation, and lower limb neuromuscular
control. Performing change of direction movements under reactive conditions
in turn imposes considerably different sensorimotor control challenges
(Gamble 2011c). The greater complexity of the neuromuscular control
challenge when the same change of direction task is performed under reactive
conditions is reflected in measurably different movement kinetics and
kinematics (Besier et al. 2001).
In addition to the sensory and cognitive abilities involved in reacting to a
stimulus and initiating the movement response, the constraints of the agility
task may also demand elements of anticipation and decision-making. For
example, when intercepting a ball it is demonstrated that skilled performers
often employ a predictive movement strategy which is initiated in advance
based on the anticipated trajectory of the ball (Gillet et al. 2010). Players at
elite level are observed to possess a superior ability to detect, select and
process ‘task relevant’ cues that are available in the competition environment
(Holmberg 2009). Following the anticipatory movement response, players will
also modify and refine their movement based on the actual observed
trajectory of the ball, and these adjustments comprise further visuo-motor
abilities which similarly differentiate performers at elite level (Gillet et al.
2010). The coupling of perception and action during agility movements is
therefore highly refined in elite players, and also highly specific to the
constraints of the given situation faced by the player in a match context
(Gamble 2011c).
Elements of speed development
A number of different elements contribute to speed performance during
competition. Each component can be viewed as an avenue for development
through which overall speed expression may be improved. It follows that each
element should be addressed via dedicated training in order to maximise
overall speed development. A multidimensional approach to developing sports
speed therefore appears the most appropriate – in much the same way as the
‘mixed methods’ approach for developing power (Newton and Kraemer 1994)
described in Chapter 6.
Technical and kinematic aspects of speed expression over the first few steps
differ from what is observed with maximum speed sprinting over longer
distances (Delecluse 1997). First-step quickness (0–5m split sprint time) and
acceleration (10m speed) have been identified as distinct capabilities to 30m
speed in sports players (Cronin and Hansen 2005). Whilst first-step quickness
and acceleration measures correlate closely to each other (r=0.92) in team
sports players (professional and semi-professional rugby league players), the
relationship with maximal speed scores was much weaker in these players
(Cronin and Hansen 2005). It follows that these capabilities must not only be
assessed independently but also that developing each of these qualities will
require a different training stimulus to speed over longer distances (Cronin
and Hansen 2005). Given the importance of speed over short distances in team
sports, it follows that dedicated training to develop the technical and
neuromuscular aspects that underpin players’ acceleration capabilities is
warranted (Cronin and Hansen 2006).
Strength and speed-strength training modes
Maximum strength and speed-strength (‘explosive power’) are key factors
from the point of view of overcoming the player’s own inertia particularly
when initiating high-velocity movements. By increasing the force-generating
capacity of the muscles involved, it is possible to improve players’ acceleration
and speed when engaging in high-velocity locomotion during a game (Cronin
and Hansen 2006; Hoff 2005). One aspect of achieving this is through the use
of appropriate strength training incorporating specific movements
(Verkhoshansky 1996).
Different strength qualities appear to predominate in different phases of a
sprint (Young et al. 1995). Maximum strength, relative to body mass, is
suggested to be relatively more important for the initial acceleration phase
(Young et al. 2001a). Concentric speed-strength capabilities appear to be
important for both initial acceleration (Young et al. 1995) and speed over
longer distances (Young et al. 2001a). As the player attains higher velocity and
foot contact time becomes shorter, reactive strength has an increasing role
(Young et al. 2001a). Fast stretch-shortening cycle abilities are similarly
critical during maximal sprinting.
Correlation studies report that measures of speed-strength are closely
related to speed capabilities of team sports players. In one study of semi- and
full-time professional rugby league players, only scores on loaded jump squat
and vertical jump (squat jump and countermovement jump) differentiated
between ‘fast’ and ‘slow’ groups within the players studied (Cronin and
Hansen 2005). In another study of professional rugby league, higher force
speed-strength measures (higher load jump squats and 3-RM hang clean)
showed strongest relationships to speed performance in the players studied
(Baker and Nance 1999). A more recent study reported that players’ scores on
hang power clean successfully differentiated between those with differing
sprinting ability (fast versus slow groups) in a sample of professional
Australian rules football players (Hori et al. 2008).
The muscles that extend the hip and knee and plantarflex the ankle are a
common focus for strength training to improve speed performance due to
their involvement in propulsion during sprinting (Deane et al. 2005; Delecluse
1997). Olympic weightlifting exercises and ballistic exercises such as jump
squat are suggested to favour lower limb speed-strength gains at appropriate
hip and knee angles for running (Cronin and Hansen 2006). Short-term
training employing Olympic-style lifts was shown to elicit improvement in
10m speed with physically active male college students with strength-training
experience (Tricoli et al. 2005). This is supported by the correlations between
hang clean and jump squat 3-RM with 10m and 40m sprint scores of rugby
league players (Baker and Nance 1999).
However, despite the importance of speed-strength of the locomotor
muscles inferred from the correlation studies mentioned previously, very few
strength and speed-strength training studies consistently report such gains in
speed measures. One reason suggested for this finding is that speed-strength
training studies use ballistic exercises and/or Olympic-style lifts that are
typically bilateral and involve predominantly vertical force production (Young
2006). This raises obvious questions concerning biomechanical and kinematic
specificity, given that sprinting involves cyclic unilateral motion and features
primarily horizontal force production. Based upon this contention two
suggestions can be made: the first is that progression to unilateral and split
variations of the Olympic-style lifts and ballistic speed-strength exercises may
be necessary to translate gains in speed-strength to sprinting performance.
The second is that horizontal speed-strength and plyometric movements –
such as unilateral bounding exercises – may develop speed-strength and
reactive strength in a way that offers greater transfer to speed performance
(Young 2006).
Sprinting-specific plyometrics
Different phases of a sprint rely on slow (300–500ms) and fast (100–200ms)
stretch-shortening cycle (SSC) properties to different degrees, depending on
duration of foot contact. Slow SSC performance will be required during the
longer foot contacts featured during acceleration. Fast SSC then predominates
as foot contacts become shorter as the player attains higher velocities.
Measures of fast SSC performance are significantly related to sprint
performance over 30m, and over longer distances (100m and beyond) in
trained athletes (Hennessy and Kilty 2001). In fact, drop jump for height was
shown to be the single biggest predictor of sprint performance in the elite
female sprint athletes studied.
Specific sprint drills and bounding exercises are the tools typically
employed to develop stretch-shortening cycle performance. To account for
specificity in order to improve transfer of training, it is important that the
force–time characteristics of exercises used reflect those experienced during
high-velocity actions on the field of play (Mero and Komi 1994). Particularly
important when developing stretch-shortening cycle performance is the
ground contact time involved with particular exercises. Excessive braking
forces and a compromised propulsion phase occur in particular with stepping
and hopping bounding exercises, which reduces the stretch-shortening cycle
training stimulus and limits their effectiveness in evoking neuromuscular
adaptations (Mero and Komi 1994).
A factor in this is that stepping and hopping bounding exercises involve
initial contact with the heel, rather than midfoot as occurs in maximal
running – which is again unfavourable from a biomechanical specificity
viewpoint. Maximal bounding that features initial contact at the midfoot and
shortened ground contact times avoids these problems and so is likely to
favour stretch-shortening cycle and neuromuscular adaptations (Mero and
Komi 1994). In support of this contention, short-term plyometric training that
featured unilateral and horizontal bounding exercises was reported to be
successful in improving 10m (acceleration) and 100m (maximum speed) sprint
times, albeit in non-athlete subjects (Delecluse et al. 1995).
Resisted co-ordination training modes
One approach employed to specifically develop acceleration involves the use
of resisted sprinting methods (Cronin and Hansen 2006). This may be achieved
simply by using an inclined surface. The kinematic changes associated with
uphill sprinting – including greater trunk flexion and reduced distance
between centre of gravity and foot strike – serve to lengthen the propulsive
phase during foot contact (Paradisis and Cooke 2001). Such changes would
appear to replicate the specific mechanics associated with the acceleration
phase (Cronin and Hansen 2006), including pronounced forward lean and
greater knee extensor involvement (Delecluse 1997).
Towing weighted sleds or tyres can similarly be used to provide resistance
for short-distance straight-line sprinting. Applying resistance in this way
demands greater stabilisation of the trunk and pelvis, and should therefore
promote development of lumbopelvic stability during the sprinting action
(Cronin and Hansen 2006). Towing tends to produce similar kinematic
changes to those described with uphill sprinting (greater trunk lean, hip
flexion and ground contact time) (Lockie et al. 2003), which may be beneficial
to developing acceleration. Heavier towing loads appear to interfere with
sprinting mechanics to a greater degree (Lockie et al. 2003). For this reason,
lighter loads (approx 10 per cent body mass) are typically recommended –
however, the friction provided by the running surface is another contributing
factor that is harder to quantify (Cronin and Hansen 2006). An alternative and
possibly more practical approach is to assess the degree to which a given load
impacts upon performance (sprint times). The guideline suggested is that if
sprint times are affected by more than 10 per cent the loading is too great and
should be adjusted (Cronin and Hansen 2006).
Adding weight to the athlete is another means by which coaches have
increased resistance during speed training (Cronin and Hansen 2006).
Weighted vests provide a different form of overload by imposing greater
vertical (rather than horizontal) forces. Although step length and step
frequency are reduced and stance times are increased, joint kinematics are not
significantly different when sprinting with weighted vests, which lends
support to the biomechanical specificity of this training mode (Cronin and
Hansen 2006).
Specific speed development
Sprinting is a highly complex skilled movement involving high degrees of
activation of multiple muscle groups (Ross et al. 2001). Speed is also
categorised as a relatively closed skill, with predictable and planned motor
patterns that can be reinforced via training (Young et al. 2001a). The relative
sequencing of muscle activation and resulting movement mechanics are
observed to change with sprint training (Ross et al. 2001). Dedicated
neuromuscular training to develop the requisite inter-muscular co-ordination
is therefore critical for improving the specific timing and execution of the
motor patterns associated with high-velocity locomotion.
Acceleration phase speed development
From a kinetic and kinematic specificity viewpoint, training methods to
develop acceleration should aim to replicate the characteristic stride
mechanics of the acceleration phase, such as the greater hip and knee flexion
at touchdown and greater knee extensor involvement in propulsion (Cronin
and Hansen 2006). In addition, the following elements should be emphasised
during acceleration technique drills, particularly during the initial strides:
• Rearward arm drive (ipsilateral side to the knee driving forwards) past
midline of the body;
• Contralateral arm swing in a forwards direction – analogous to the arm
swing employed during the propulsion phase of a vertical jump;
• Body lean angle approaching an angle of 45 degrees from the vertical at ‘toe
off’ for standing starts, or in the range 30–40 degrees for rolling starts
(Kugler and Janshen 2010);
• ‘Full’ extension of hip, knee and ankle so that there is a straight line from
rear foot to the top of the head at ‘toe off’.
Falling starts are a good tool to familiarise the player with the desired degree
of forwards body lean employed during acceleration movements. The threepoint crouch start similarly offers a means to develop co-ordination of arm
action and leg drive from a flexed starting position. Progressions for standing
start drills will also include a variety of starting strategies employed by
players to achieve the desired forwards body lean and foot placement. For
example, one such strategy involves stepping back, also known as the ‘false
step’, in order to create a forwards lean and position the supporting foot
behind the athlete’s centre of mass (Frost et al. 2008). These movement
strategies can also incorporate a preload action, such as a drop step, which can
serve to enhance power output and thereby propulsion – in a similar fashion
to the ‘split step’ employed by racquet sports players to improve first step
acceleration (Gamble 2011b).
Another important consideration is the conditions from which acceleration
and first-step quickness are initiated during matches (Young et al. 2001a).
Players may be static or in motion (in a variety of directions) when they
accelerate to intercept the trajectory of a ball or become involved in play.
Players must therefore be capable of executing acceleration and developing
short-distance speed from a variety of starting conditions (Cronin and Hansen
2006). For similar reasons, in addition to conventional standing starts,
acceleration techniques should be developed from different postures and
positions, and also rolling starts to develop the ability to accelerate whilst in
motion. Finally, execution of these different acceleration techniques under
reactive conditions should be included in order to develop the coupling of
perception and action during acceleration movements (Gamble 2011b).
Maximal speed development
A key aspect of improving sprint running velocity is maximising the
propulsive ground reaction force at each foot contact and limiting touchdown
time (Hunter et al. 2005). Propulsive impulse generated by the athlete during
touchdown, relative to their body mass, is the single biggest predictor of
sprinting velocity over short distances (≈16m) (Hunter et al. 2005). Coordinating torque generation at the hip and knee and the orientation of the
foot prior to and during touchdown is a complex neuromuscular skill – it
follows that this should require dedicated training in order to develop it.
Accordingly, high-velocity training aimed at enhancing motor unit
recruitment (intra-muscular co-ordination) and inter-muscular co-ordination
has been shown to elicit improvements in speed performance (Delecluse et al.
1995). Indeed, conventional sprint training appears to be the superior method
for producing short-term improvements in technique and speed (Kristensen et
al. 2006).
Particular technical aspects of straight-line sprinting can also be coached
and reinforced by appropriate technique drills (Cissik 2005). By their nature,
such drills are self-paced and carried out at submaximal speed. Examples
include walking drills such as ‘A’ drills (developing static balance), and ‘B’
drills (dynamic balance development from a static base of support) commonly
employed in track athletics. A variety of progressions exist for these drills,
which include bounding or skipping variations. It is critical to develop the
ability to maintain a stable balanced position from which to generate and
direct ground force reaction forces to produce propulsion. Similarly, these
drills offer a means to develop the required postural control and co-ordination
to maintain vertical stiffness throughout the lower limb kinetic chain and
torso during the stance phase and avoid any collapse during each foot contact
(Nummela et al. 2007). The other role served by these technique drills is to
instruct and reinforce correct ‘recovery’ mechanics during the transition
between the end of the stance phase (that is, ‘toe off’) and the early–middle
part of the swing phase. Specifically, these drills emphasise flexing the leg as it
travels under the body in order to reduce the moment of inertia (van Ingen
Schenau et al. 1994).
While the technique drills described allow particular aspects of sprinting
mechanics to be emphasised, such drills remain markedly different from the
kinematics and movement velocities characteristic of high-speed running.
Therefore, in order to allow carry-over to performance, these technique drills
must ultimately be progressed to actual sprinting (Cissik 2005). It is important
that players are regularly exposed to sprinting at maximal velocity, as
neuromuscular co-ordination patterns for individual muscles are observed to
differ when running at different velocities (Higashihara et al. 2010). Sprint
practice undertaken by players in different positions should also reflect the
velocities and distances encountered during competitive matches.
Furthermore, for sports that involve carrying or dribbling a ball, specific
practice of high-speed locomotion accommodating the ball or implement of
the sport should also be accounted for when designing speed-training sessions
(Fujii et al. 2010; Sheppard and Young 2006).
Elements of agility development
A categorical definition of agility has recently been offered: ‘rapid whole-body
movement with change of velocity or direction in response to a stimulus’
(Sheppard and Young 2006). In the context of team sports, agility therefore
comprises not only change of direction abilities but also perception and
decision-making. In much the same way as speed expression, agility in the
context of team sports is multifactorial (Gamble 2011c). There are also
additional aspects to consider in the case of change of direction movements,
such as the need to decelerate and accelerate in various directions.
Fundamentally, team sports agility likewise comprises reaction to gamerelated cues, ‘perception–action coupling’ and decision-making elements
(Sheppard and Young 2006).
There are two major schools of thought regarding ‘sports agility’
development (Bloomfield et al. 2007). One approach involves relatively closed
skill practice of movement mechanics, often using specialised commercially
available equipment such as ladders, mini-hurdles and resistance belts. Others
advocate a more open skill approach in which agility movements are
conducted in a training environment that is less structured and thereby closer
to match conditions (Bloomfield et al. 2007).
Strength and speed-strength training modes
Lateral movements are a characteristic aspect of movement during team
sports performance. In particular, evasive manoeuvres that occur in
competitive play are frequently initiated with a lateral step (Twist and
Benicky 1996). Similarly, the sidestep cutting action (rapid change of direction
to evade a defensive opponent) involves hip abduction and generation of
medial-lateral ground reaction forces to create lateral propulsion (McLean et
al. 2004). Speed-strength development in these different planes of motion
would therefore appear important to develop lateral acceleration in much the
same way as sagittal plane speed-strength exercises are employed to improve
straight-line acceleration (Hedrick 1999).
It is reported that standard bilateral strength and power measures (squat,
loaded and unloaded vertical jump) typically are not strongly related with
change of direction performance (Sheppard and Young 2006). Hang power
clean scores of Australian rules football players were similarly unrelated to
these players’ scores on a change of direction measure (Hori et al. 2008). The
bilateral and predominantly sagittal plane movement that characterises
exercises typically used for speed-strength development therefore appear
inadequate for developing the requisite strength capabilities for change of
direction movements. Strength (both concentric and eccentric), speed-strength
and reactive strength qualities required for change of direction movements
may be better developed via appropriate unilateral strength and plyometric
training exercises (Twist and Benicky 1996). Similarly such training should
necessarily feature force-generation and propulsion movements in the
relevant planes of motion. This is an area that warrants further research.
Figure 7.1 Cable resisted cross-over lateral lunge
Depending on the duration of ground contact during these movements,
slow SSC elements will also contribute to performance. Slow SSC elements
(300–500ms) are likely to be more important than fast SSC (100–200ms) due to
the relatively longer foot contacts involved in change of direction movements
in comparison to sprinting. Reactive strength measures (for example, drop
jump test scores) do appear to have stronger statistical relationship with
change of direction performance than concentric strength measures, which
typically show no significant relation to change of direction ability (Sheppard
and Young 2006). For this reason, it is suggested that specific training to
develop these muscular properties, such as bilateral and unilateral drop jump
training, have the potential to improve change of direction abilities (Young
and Farrow 2006). Such training to develop reactive strength should also
feature single-leg plyometric drills that involve reversing direction and
incorporate lateral movement in order to account for the relevant movements
involved in change of direction.
Postural control and stability
Lumbopelvic stability and neuromuscular control aspects that include wholebody proprioception and balance all contribute to the ability to change
direction efficiently. The player’s awareness of, and ability to control, the
position of their centre of mass is critical in allowing them to efficiently
perform agility movements (Yaggie and Campbell 2006). The ability to retain
lumbopelvic stability and strong trunk posture would seem to be crucial to
maintain proper lower limb mechanics and efficient transfer of force from the
ground upwards to generate change of direction movement (Kibler et al.
2006). Dynamic balance capacities are also important to allow the player to
more effectively dissipate impact forces involved in deceleration and change
of direction movements (Myer et al. 2006a).
Figure 7.2 Alternate leg lateral box skips
Whatever starting posture movements are initiated from, acceleration,
deceleration and changes in direction require appropriate postural
adjustments (Young and Farrow 2006). A key aspect of postural control with
respect to change of direction movement is controlling the position and
orientation of the trunk with respect to the pelvis (Kibler et al. 2006). For
example, during a lateral cutting manoeuvre the player typically leans into the
new direction of movement as they cut with their outside foot, in order to
maximise horizontal propulsion. Similarly, optimal execution of movement
requires the player to maintain tension through a stable torso in order to
transmit forces generated through the ground to effectively transfer these
ground reaction forces into movement (Young and Farrow 2006). As such,
stabilisation and strength through the lumbopelvic region would appear
critical to optimal function of the kinetic chain (from base of support to
extremities) involved during athletic movements in general, and change of
direction movements in particular (Kibler et al. 2006).
Planned change of direction movements enable the athlete to anticipate,
which allows the required postural adjustments to be made much more easily.
In the case of unanticipated cutting movements that are executed in response
to an external cue, these postural adjustments are harder to make, which in
turn affects loading on lower limb joints (Besier et al. 2001). It follows that
postural adjustments under reactive conditions should be incorporated into
players’ training (Besier et al. 2001; Craig 2004).
Change of direction movement skills development
Specific change of direction training has been shown to carry over to change
of direction performance tests – particularly those involving similar cutting
angles (Young et al. 2001a). Drills that integrate specific lateral and cutting
movements allow technique to be developed and specific neuromuscular
patterns to be reinforced (Craig 2004). This approach is analogous to the
programmed conditioning methods for agility development described by
Bloomfield and colleagues (2007).
By the nature of team sports, players are frequently required to decelerate
sharply, as they respond to the movement of team-mates, opponents and the
ball (Lakomy and Haydon 2004). A player’s ability to decelerate is important
in executing change of direction movements (Griffiths 2005), as they must first
brake their forward momentum before propelling the body into the new
direction of movement (McLean et al. 2004). Despite this, deceleration is not
commonly addressed during training for team sports (Lakomy and Hayden
2004; Griffiths 2005). Targeted neuromuscular training to develop technical
aspects of deceleration is therefore an area that may warrant investigation for
team sports players.
Initially simple cones may be used to mark changes of direction. It has been
identified that the specialised equipment commonly used in conjunction with
programmed ‘agility’ conditioning methods are in fact not crucial to the
success of these training modes (Gamble 2011c). Drills involving specialised
equipment can be readily substituted for equivalent drills that develop similar
movement skills without any significant impairment of performance
improvements observed following training (Bloomfield et al. 2007). For
example, in place of ladders the line markings on the pitch or court can be
used to guide footwork drills. Indeed, this approach may be preferable as
players will be less inclined to look at the floor when these drills are
performed without ladder apparatus.
This can be progressed to using static poles or standing players to simulate
a defender. A recent study found that the presence of even a static dummy
‘defender’ had a marked influence upon sidestep cutting mechanics (McLean
et al. 2004). The simulated defender (a model skeleton) caused the players to
perform more forceful cutting movements (greater ground reaction forces),
accompanied by more hip flexion and abduction as well as greater (flexion
and valgus) angles at the knee (McLean et al. 2004). These self-paced drills can
be progressed by incorporating game-related skill movements (Twist and
Benicky 1996).
A further progression is to initiate cutting movements in response to a
particular external cue. Movement mechanics and joint kinematics during preplanned and unanticipated cutting movements are significantly different
(Besier et al. 2001). It follows that unanticipated cutting must be addressed in
training, in order for neuromuscular control and co-ordination abilities to
carry over to agility movements executed in match situations. This need for
perception–action coupling and decision-making elements is explored further
in a later section.
Arm action is an often overlooked component of agility that can have a
pronounced effect on the athlete’s efficiency of movement when changing
direction (Brown and Vescovi 2003). A key aspect during the sidestep cutting
action (manoeuvre commonly used to evade an opponent) is driving the inside
arm in the opposite direction to assist driving the inside leg towards the new
direction of movement as the player executes the ‘cut’ with their outside foot.
After this first stride in the new direction, similar backward arm drive by the
opposite (outside) arm then assists in rotating the body and bringing the
outside leg through to drive towards the new direction of movement. In both
the initial cutting stride and second stride it is important that the arm drive is
kept tight to the body, in order to reduce unwanted inertia and to direct the
acceleration forces in the desired direction (Brown and Vescovi 2003). These
elements must be addressed by specific movement practice in much the same
way as any other movement skill.
For sports that involve carrying a ball (American football, rugby football) or
holding an implement (field hockey, lacrosse, ice hockey) there are indications
that skill sports athletes exhibit enhanced agility when holding the implement
of their sport (Kraemer and Gomez 2001). This is something that must be
considered when designing agility training in these sports. With progression
of training, it follows that drills can become more sport-specific by
incorporating a ball or sports implement in the drill (Jeffreys 2006; Sheppard
and Young 2006).
Transfer training for agility development
There is an important distinction between change of direction abilities during
movements that are pre-planned (such as manoeuvring around fixed
obstacles) and sport-specific agility executed in response to game-specific cues
(movement of the ball, opponents or team-mates) (Sheppard and Young 2006;
Young and Farrow 2006). During the initial stages of training to develop
agility, change of direction movements that feature in agility performance can
be developed by repetition of specific movement skill drills that are self-paced
and negotiate fixed obstacles (cones, slalom poles, and so on). This change of
direction training is essentially closed skill practice as movements are preplanned and do not require any reaction or decision-making (Sheppard and
Young 2006).
However, the defining characteristic of agility is that change of direction or
velocity occurs in response to an external stimulus (Sheppard and Young
2006). As such in order to develop agility, planned change of direction
movements executed in a static practice environment must be progressed to
open skill conditions (i.e. requiring response to a stimulus) (Craig 2004).
Requiring the athlete to initiate movements and changes of direction in
response to external cues provides specific agility training as opposed to preplanned change of direction movements (Young and Farrow 2006). Such
training is important to improve reaction time and the ability to interpret cues
from the environment in order to make postural adjustments and improve
movement execution. These abilities also have implications in terms of injury
prevention: loads sustained at the knee are reported to be significantly
increased during unanticipated cutting movements (Besier et al. 2001).
Appropriate dynamic neuromuscular training emphasising postural control
and correct lower limb alignment during unanticipated cutting manoeuvres
(such as against a ‘live’ opponent) therefore appears necessary in order to
protect against non-contact knee injury (Besier et al. 2001).
How this transition to specific agility development can practically be
achieved is by progressively removing the player’s ability to anticipate
movement responses (Besier et al. 2001). This progression can be viewed as a
continuum of motor learning drills with closed movement skill practice at one
extreme, and an entirely random open skill environment at the opposite end
of the spectrum. In between these two extremes, strength and conditioning
specialists can implement a continuum of drills that expose the player to a
progressively increasing perceptual challenge. Examples of progressions
include self-paced to maximal execution speed; progressing from fixed
obstacles to initiating pre-planned movement on command; simple reaction
(single response) to complex reaction (multiple movement responses); and
finally incorporating decision-making and read-and-react drills against a ‘live’
opponent.
With advances in agility training, appropriate constraints associated with
the particular sport should also be replicated in the training environment, such
as opposing players and dimensions of the playing area (Handford et al. 1997).
Similarly, making the cues in read-and-react drills game-related and
incorporating decision-making that is specific to the sport may further help
translate change of direction speed into sport-specific agility (Handford et al.
1997; Young et al. 2001a). In designing these open skill ‘read-and-react’ drills,
sport-specific cues and movement responses must first be identified for the
sport and playing position (Jeffreys 2006). These abilities to anticipate and
process cues from the game environment in order to make decisions quickly
are identified as a key factor in the faster movement times of more skilled
players (Young and Farrow 2006). However, at the open skill end of the
spectrum it may be argued that such advanced cognitive skill acquisition is
better suited to the domain of technical and/or tactical practice and
competitive play, under the instruction of the sports coach.
Summary
A number of individual qualities contribute to expression of speed qualities.
Speed-strength development appears important in enabling players to
overcome their own inertia when initiating high-velocity movements;
however, modified versions of conventional speed-strength training modes
may offer superior transfer to speed performance. Plyometric training can
develop stretch-shortening cycle components that contribute to speed
performance – specifically, slow SSC during acceleration and fast SSC for
maximal speed; such training should have appropriate emphasis on unilateral
and horizontal bounding exercises.
In addition to improving force-generating capacity via speed-strength
training, acceleration abilities can also be developed by employing specific
acceleration training modes. Whether developing acceleration or maximal
speed, neuromuscular aspects – in particular inter-muscular co-ordination –
can be developed via specific technical training, which will necessarily include
actual sprinting over appropriate distances. In view of the multifactorial
nature of speed expression, an integrated approach to players’ speed training
that accounts for each of the aspects described would appear to be the best
route to optimal development of overall speed performance.
In much the same way as straight-line speed development, multiple
components contribute to agility performance in team sports. Again,
dedicated training for each of the components described is required to fully
exploit all of the identified factors that may contribute to improving agility
performance. Postural control, neuromuscular skill, lateral acceleration,
deceleration and reactive strength qualities are all implicated in successful
execution of the change of direction movements involved in agility
performance. Addressing the perceptual aspects, stimulus-response, and
decision-making elements that characterise agility represents an additional
challenge that must be accounted for in order to specifically develop agility.
Essentially, developing all these elements will comprise both approaches
typically taken to sports agility development (Bloomfield et al. 2007) –
including aspects of closed skill practice and ultimately progression to an open
skill practice environment.
8
LUMBOPELVIC ‘CORE’ STABILITY
Introduction
Core stability training has become an integral part of training for all athletes
with the aim of improving performance (Carter et al. 2006; Liemohn et al.
2005), and core exercises are commonly prescribed for therapeutic training
applications (Brown 2006). Specificity of training has a number of implications
with regard to the transfer of core training modes to different training
outcomes, for example performance versus injury prevention or rehabilitation.
Core stability is described in the sports medicine literature as ‘the product
of motor control and muscular capacity of the lumbo-pelvic-hip complex’
(Leetun et al. 2004). In musculoskeletal terms this comprises the spine, pelvis
and hip joints, and proximal lower limb – in addition to all associated
musculature (Kibler et al. 2006). For example, there are 29 individual muscles
that attach on the pelvis. Furthermore, the combination of muscles that
provide lumbopelvic stability in a particular posture or movement is shown to
vary depending on factors such as posture and the constraints of the task
(Juker et al. 1998). The global term ‘core’ could therefore refer to any of a
number of independent components that contribute to providing stability to
the lumbopelvic region under various conditions (Mendiguchia et al. 2011).
Training the ‘core’ is therefore considerably more complex than the global
term core training implies. Given the complexity of the structures and joints
of the lumbar spine, pelvis and hip girdle, and the number of different muscles
involved, it perhaps should not be surprising that developing lumbopelvic
stability comprises a host of different factors. In reality, the term ‘core
training’ has become an all-purpose label for any exercise that addresses some
aspect of lumbopelvic stability (Gamble 2007a).
This ambiguity is likely behind the confusion regarding the effectiveness of
‘core training’ for different health and performance goals (Stanton et al. 2004;
Tse et al. 2005). Training for lumbopelvic stability is typically undertaken with
one of two objectives: improving performance and injury prevention (Kibler et
al. 2006). The efficacy of ‘core training’ modes for injury prevention is
documented; however, support for the role of training for lumbopelvic
stability for performance enhancement has proven to be more elusive.
The various functions of the ‘core’
When stripped of muscle and left to rely upon passive (bone and ligament)
support, the human spine will collapse under 20lb (≈9kg) of load (Barr et al.
2005). This illustrates that the spine depends heavily upon the active stability
provided by various muscles (Cholewicki and McGill 1996). The combination
of systems and muscles that act to provide stability varies with posture, the
direction of movement and magnitude of loading on the spine (Juker et al.
1998). Hence, a wide variety of muscles contribute to different degrees
according to the demands of the situation.
In addition to providing spine stability under static conditions, lumbopelvic
stability is identified as critical for whole-body dynamic balance (Anderson
and Behm 2005). Most of the muscles that move and stabilise the limbs attach
proximally to the lumbo-pelvic-hip complex. The muscles of the ‘core’
collectively function as synergists for athletic activity (McGill 2010). The
‘core’ region is therefore described as the ‘anatomical base for motion’ (Kibler
et al. 2006). Movements in sports occur in multiple directions; there is
accordingly a demand for lumbopelvic stability in all planes of motion (Leetun
et al. 2004).
Furthermore, the lumbar spine is the site through which various
compressive and shearing forces are transmitted during activity (Cholewicki
and McGill 1996; Stephenson and Swank 2004). Co-contraction of various
lumbopelvic muscles serves to stiffen the spine and trunk region (McGill
2010). This serves to allow efficient transfer of forces from the ground to
produce movement and/or generate torque at the extremities (Behm et al.
2005; McGill 2006c).
It has been demonstrated that submaximal levels of muscle activation are
usually adequate to provide effective spine stabilisation (Cholewicki and
McGill 1996). Continuous submaximal muscle activation therefore appears to
be crucial in maintaining spine stability for most daily tasks (McGill 2007b).
Measures of trunk muscle endurance therefore show the greatest relationship
with spine stability and incidence of pain or injury (McGill 2006b).
Conversely, under higher-force conditions the larger muscles must brace the
trunk whilst generating propulsion and resisting unwanted motion; this in
turn demands various strength qualities.
Components of lumbopelvic stability
There are a number of different systems which can contribute to providing
stability to the lumbo-pelvic-hip complex under a given set of conditions.
Each of these components can be involved in various combinations,
depending upon the constraints of the task and the loading conditions
involved. Key factors that will determine the contribution from each system
include the following:
• postural aspects – in particular whether the athlete is in a weight-bearing
stance;
• the degree of any upper limb involvement;
• what motion is occurring at the trunk and extremities;
• the internal and external loading conditions imposed upon the athlete.
Deep postural muscles of the lumbar spine and pelvic
girdle
The deep lumbar spine stabiliser muscles have attachments at segmental level
(Anderson and Behm 2005; Barr et al. 2005). The most widely recognised of
these muscles are transversus abdominis and multifidus; however, these
muscles also include other muscles, such as rotatores (McGill 2007a). These
muscles are small, which limits their torque-generating capacity, and are thus
mainly concerned with providing local support. Hence these deep postural
muscles have been collectively termed the ‘local stabilising system’ (Carter et
al. 2006; Liemohn et al. 2005).
A reflection of the postural function of these muscles is that they are
observed to fire at a low level (≈10–30 per cent of maximum) in a tonic
fashion for prolonged periods; that is, these muscles do not fatigue in the same
way as the more superficial muscles (Barr et al. 2005). These muscles are also
shown to contain a high density of receptors (McGill 2007a). This reflects their
role in collectively providing proprioceptive sense of the position and
orientation of the pelvis and lumbar spine.
Segmental control of the lumbar vertebrae and the orientation of the pelvis
also strongly influences the loading imposed on the lumbar spine and the
activity of these muscles is identified as critical for spine stability (Cholewicki
and McGill 1996). The importance of these muscles can be inferred from the
finding that these muscles are atrophied in individuals with chronic lower
back pain (Barr et al. 2005; Danneels et al. 2001).
The capacity to control lumbar spine posture, and the positioning and
orientation of the pelvis in particular, serves a critical role in determining the
ability of other muscles that stabilise the lumbo-pelvic-hip complex to
function (Workman et al. 2008). In particular, an anterior pelvic tilt is to be
avoided given that this adversely affects the function of other muscles
especially the muscles of the hip girdle. A posture characterised by an anterior
tilt of the pelvis (and the lumbar spine lordosis that results) is also associated
with low back pain and groin pain and/or injury (Waryasz 2010).
Maintaining ‘neutral’ lumbar spine posture, and controlling the position
and orientation of the pelvis in all three planes/axes of motions, is therefore
critical to any activity. Engaging the deep local stabiliser muscles must be
viewed as fundamental to all activities undertaken in training and
competition, regardless of what other subsystems are recruited on top.
The cues or techniques that are employed when teaching athletes to engage
the deep postural muscles will however have a profound effect on spine and
lumbopelvic stability. Specifically any technique that encourages abdominal
hollowing or cues that involve ‘drawing the belly button closer to the spine’
should be avoided (McGill 2007c). The cues or techniques coached to athletes
should therefore ensure that the shape or surface geometry of the abdomen is
unchanged as they engage the deep postural muscles. In this way these
muscles can be recruited in a way that does not compromise the function of
the larger muscles that will be required to brace the trunk during higher-force
athletic activities.
Muscles and connective tissue structures of the trunk
The muscular component of this subsystem includes the larger and more
superficial muscles of the abdomen, including rectus abdominis and internal
and external obliques, and the muscles of the back, which include the large
extensor muscles longissimus and iliocostalis. These muscles, together with
the thoracolumbar fascia (the abdominal fascia at the front, the lumbodorsal
fascia at the back), collectively form a ‘corset’ structure (McGill 2007a).
Co-activation of these various muscles causes tension to be applied via the
connective tissue structures, which serves to create a rigid corset surrounding
the trunk (McGill 2007a). This natural corset of muscles and connective tissues
acts in this way to brace the trunk and lumbar spine. During this bracing
action the co-contraction of internal and external obliques, together with
transverse abdominis, provides a cross-bracing effect that generates hoop
stiffness and stability along various axes (McGill 2007c).
The larger abdominal muscles also assist with generating movement at the
trunk; for example, the internal and external obliques are implicated in both
twisting and lateral bending movement (McGill 2007a). That said, typically
such movement predominantly originates from the supporting limb(s).
Muscles of the shoulder complex
Due to their attachment to the lumbodorsal fascia, the larger muscles of the
shoulder girdle (for example, latissimus dorsi, trapezius) are able to contribute
to providing tension and rigidity to the ‘corset’ structure described above
(Pool-Goudzwaard et al. 1998). In this way the muscles of the shoulder girdle,
particularly those associated with the articulation between scapula and
thorax, contribute to bracing the trunk during high-force activities (McGill
2007a).
Figure 8.1 Alternate arm cable lat pulldown
In addition, when the athlete is load-bearing through the upper limb(s) the
muscles of the scapula and rotator cuff are implicated in stabilising the
shoulder girdle, and in turn the trunk region as a whole. During closed chain
upper limb actions particularly, for example a push up exercise, these muscles
will allow the athlete to anchor the shoulder girdle from the supporting upper
limb, in much the same way as described below with regards to the muscles of
the hip girdle.
Muscles of the hip girdle
The hips serve as the anatomical base of support for the pelvis and trunk. One
of the primary functions of the muscles of the hip girdle is to stabilise the
pelvis from the supporting lower limb (Kibler et al. 2006). Although the
ligamentous structures of the hip provide a great deal more support than is the
case with the shoulder (glenohumeral) joint, the muscles of the hip girdle
nevertheless work in a way that is analogous to the rotator cuff muscles of the
shoulder (Fabrocini and Mercaldo 2003). These hip muscles essentially allow
the athlete to anchor the pelvis from the supporting lower limb, which in turn
provides a stable platform for the lumbar spine and the trunk as a whole
(McGill 2007a).
The other major function of the hip muscles is generating and transmitting
forces to the trunk from the supporting limb(s) in order to generate
movement. In addition to their role in normal walking and running gait, these
muscles are crucial to generating torque and movement during pivoting and
twisting actions. For example, gluteal activation was found to have a
significant role during the throwing action in a study of baseball pitchers
(Oliver and Keeley 2010). Activation of gluteal muscles (gluteus maximus and
gluteus medius) was also found to directly relate to pelvis kinematics (rate of
axial rotation) during the throwing action.
Summary
Lumbopelvic stability is clearly multidimensional; McGill (2006) has
elucidated that the diverse muscle groups which combine to support the
lumbar spine must be in balance in order to ensure optimal stability is
provided. Given the complexity of the structures and joints of the lumbar
spine, pelvis and hip girdle, and the number of different muscles involved, it
perhaps should not be surprising that developing lumbopelvic stability
comprises a host of different factors (Gamble 2007).
The function of the core relies upon the integration of a number of different
components (Borghuis et al. 2008). Neuromuscular control aspects that govern
the recruitment of these various systems and co-ordination of individual
muscles are therefore critical. For example, maintenance of lumbopelvic
stability during dynamic movements is underpinned by the firing of various
core muscles in preparation for movement (Barr et al. 2005; Leetun et al. 2004).
Hereby, the muscles providing the base of support are activated before the
muscles involved in the particular movement (Anderson and Behm 2005).
These anticipatory postural adjustments help to prevent unwanted trunk
motion and provide a stable base of support during movement. The
neuromuscular system must govern function of stabilising muscles not only in
anticipation of expected direction and magnitude of forces, but also in
reaction to sudden movement or loading (Barr et al. 2005). A reflection of the
importance of neuromuscular control is that individuals with chronic lower
back pain exhibit impaired neuromuscular feedback and delayed muscle
reaction, which is accompanied by reduced capacity to sense the orientation
of their spine and pelvis (Barr et al. 2005; Rogers 2006).
Demands placed on the ‘core’ when engaging in team
sports
In accordance with the variety of functions served by the respective
subsystems that provide lumbopelvic stability, there is equally a demand for
endurance, strength and power for the respective muscle groups involved
(Willardson 2007). For example, the challenge of maintaining postural
integrity whilst sustaining and/or generating external forces will require both
strength and endurance of different lumbopelvic muscles (Barr et al. 2005).
Furthermore, depending on the sport, these various neuromuscular control
and strength capabilities are required under both static and dynamic
conditions. Co-contraction of muscles to stiffen or buttress the spine when
performing activities under load will require strength under quasi-isometric
conditions. Throwing and striking activities often require muscles of the trunk
to assist with generating twisting torque, which demands concentric speedstrength. Conversely, deceleration and change of direction movements involve
considerable eccentric loading of the muscles of the trunk and hip girdle as
they work to resist movement generated by the athlete’s own inertia. Finally,
maintaining lumbopelvic posture and spine stability requires endurance and
in particular the ability to maintain function under challenged breathing
conditions.
Lumbopelvic stability and injury
The postural muscles that prevent excessive spine motion at segmental level,
and help maintain desired pelvis and lumbar spine posture, act to reduce the
stresses placed upon the lumbar spine and thereby protect against injury
(Danneels et al. 2001; McGill 2006c). In addition, the larger more superficial
muscles that brace the trunk and resist external forces under conditions of
higher loading also serve to spare the spine (McGill 2006c).
Lumbopelvic instability can be both the cause (McGill 2006c) and result of
injury (Hamill et al. 2008). Weakness or impairment at any point in this
integrated system of support can lead to damage to structural tissues, resulting
in injury and pain (Barr et al. 2005). As such, low or unbalanced scores on
various tests of muscle function indicative of poor lumbopelvic stability are
frequently identified as risk factors for injury (McGill 2006b). Impaired passive
stability and disrupted motor patterns (compromising active stabilisation) are
also commonly observed following injury (McGill 2006b; Montgomery and
Haak 1999). For example, neuromuscular deficits in core stability and hip
muscle function are often seen among subjects with low back pain (Hamill et
al. 2008). Addressing these aspects via appropriate training can therefore serve
a dual protective role in terms of both guarding against initial injury for
healthy athletes and reducing the risk of re-injury in those with a history of
low back pain.
A number of studies support the assertion that training different aspects of
lumbopelvic stability has a role to play in reducing incidence of injury (Barr et
al. 2005; Cusi et al. 2001; Hides et al. 2001; Tse et al. 2005). For example, scores
of trunk muscle endurance are consistently shown to correlate with incidence
of low back pain or injury (McGill 2006b). Lumbopelvic training that
incorporated Swiss ball exercises was shown to successfully improve these
measures of spine stability (extensor and side bridge endurance times) in
sedentary individuals (Carter et al. 2006).
The need for targeted interventions to reduce incidence of back injury is
underlined by the observation that the lower back is frequently reported as
the third most common site of injury in sports, after the ankle and knee
(Nadler et al. 2000). Low back pain and injury is reportedly commonplace
among both recreational and competitive athletes and can severely impair the
athlete’s ability to train and compete (Montgomery and Haak 1999). Back
injury is particularly prevalent in female athletes – injury data from NCAA
collegiate athletes during the 1997/98 season indicated almost twice the
number of lower back injuries in females compared to male athletes (Nadler et
al. 2002).
In addition to injuries directly involving the spine, lumbopelvic stability has
implications for injury risk and function of the joints of the lower extremity,
via the kinetic chain of lower limb joints from the supporting foot to the
lumbar spine (Leetun et al. 2004; Nadler et al. 2000). Consequently, deficits in
lumbopelvic stability are identified as playing a role in the mechanism of knee
ligament injury in particular (Hewett and Myer 2011). The role of lumbopelvic
control and different aspects of core stability have therefore been highlighted
as critical areas for investigation and interventions aimed at correcting
neuromuscular control deficits that predispose athletes to lower limb injury.
Contribution of the ‘core’ to neuromuscular control of
the lower limb
Muscles of the lumbo-pelvic-hip complex serve to provide ‘proximal control’
to the lower limb kinetic chain (Mendiguchia et al. 2011). Over recent years a
number of studies in the sports medicine literature have identified factors
relating to lumbopelvic stability in the mechanism for lower limb injury
(Zazulak et al. 2007). The contribution of lumbopelvic stability and control of
positioning and motion of the trunk in relation to the supporting lower limb
has recently been implicated in the mechanism for knee injury for female
athletes specifically (Hewett et al. 2009).
Differences in control of trunk posture in female athletes compared to
males have been identified during different athletic tasks. For example, female
athletes characteristically execute landing movements in an upright stance;
there is some suggestion that it is likely that female athletes exhibit associated
differences in trunk and hip muscle recruitment and activation, albeit these
data are not yet available (Mendiguchia et al. 2011). These postural traits are
identified as placing the knee ligaments, in particular the anterior cruciate
ligament or ACL, at particular risk of injury (Leetun et al. 2004). Similarly, an
impaired ability to control the positioning and motion of the trunk and
thereby the athlete’s centre of mass during change of direction movements is
shown to adversely affect torques generated at the lower limb joints (Hewett
and Myer 2011). Deficits in lateral stability of the trunk in particular have
been implicated as a major risk factor for knee ligament injury with female
team sports players during pivoting and cutting change of direction
movements (Zazulak et al. 2007).
Based upon these findings it would appear that the trunk postures adopted
by athletes in general, and females in particular, have the potential not only to
modify the loading on lower limb joints during athletic activities but also to
influence lower limb biomechanics. Training interventions to modify postural
control strategies allow more favourable positioning of the trunk and head
over the supporting limb(s) during relevant landing and change of direction
activities might therefore also confer improvements in lower limb kinetics and
kinematics (Mendiguchia et al. 2011). The hip musculature plays a key role in
supporting and controlling motion at the trunk (Hewett and Myer 2011).
Therefore, in addition to the lateral trunk muscles, developing strength and
function of the muscles of the hip girdle, in particular the abductor muscles,
should be a priority (Mendiguchia et al. 2011). Preliminary evidence from
investigations supports the efficacy of training to develop hip and trunk
neuromuscular control as a means to address knee injury risk factors (Myer et
al. 2008).
Core function and performance
The lumbopelvic region represents a vital link in the kinetic chains,
incorporating all joints and body segments from base of support to
extremities, that are involved in athletic movements (Kibler et al. 2006). From
this viewpoint, stabilisation of the lumbopelvic region would appear critical
during athletic activities and sports skill tasks. Co-contraction of various
muscles serves to stiffen the core region to facilitate efficient transmission of
forces (McGill 2010). For example, a double spike in trunk muscle activation is
observed during striking movements: the initial peak is observed as the athlete
initiates the striking action; and the second peak serves to maximise force as
the athlete connects with the target object (McGill et al. 2010).
As well as providing a stable base for motion at the distal segments (the
limbs), the ‘core’ can also be the origin from which rotational torques are
generated and transferred to the extremities (Kibler et al. 2006). For example,
during an overarm throw the sequential rotation of the hips and trunk serves
to generate angular momentum, which is transmitted to torque generation at
the shoulder joint and ultimately the throwing arm (Aguinaldo et al. 2007). It
follows that appropriate development of lumbopelvic stability and strength
should be reflected in enhanced athletic and sports performance. Based upon
such assertions coaches continue to routinely prescribe ‘core’ training with
the specific aim of improving sports performance.
Despite this, a positive link between core training interventions and
improvements in measures of athletic performance has yet to be established in
the research literature (Stanton et al. 2004; Tse et al. 2005). In part this reflects
that there a very few studies that have investigated this relationship (Hibbs et
al. 2008). Another factor is the lack of consistency in terms of what constituted
core training in the studies, and the nature of exercises employed (Gamble
2007a). Typically, investigators have failed to differentiate between core
endurance and core strength. Assessments of core stability have similarly been
conducted under conditions which represent a very limited load challenge for
a trained athlete. Despite this, some of these tests have still reported
significant, albeit weak to moderate, relationships with different measures of
performance (Nesser et al. 2008; Okada et al. 2011).
The training interventions employed in the majority of the limited number
of studies undertaken to date have likely been of insufficient intensity to elicit
increases in strength (Nuzzo et al. 2008). This factor alone may explain the
lack of any gains in performance reported by some studies (Stanton et al. 2004;
Tse et al. 2005). It has been identified that more challenging training modes,
equating to higher relative intensity and force demands, will be required to
specifically develop the core strength required for athletic performance
(McGill 2010). Preliminary support for this is provided by recent studies
featuring more demanding core training interventions which have reported
improvements in sports performance (throwing velocity) (Saeterbakken et al.
2011).
In order to maintain whole-body stability whilst sustaining and/or
generating external forces, athletes require both strength and endurance for
these muscles (Barr et al. 2005). These capabilities are required under a variety
of static and dynamic conditions during competition. Furthermore,
movements in athletic events and team sports occur in multiple directions;
accordingly, players must possess lumbopelvic stability in all three planes of
motion (Leetun et al. 2004).
An integrated approach to training the ‘core’
As has been described, there are various different subsystems involved in
providing lumbopelvic stability, and there are a variety of roles that these
muscles are required to fulfil during athletic movement. It is therefore
increasingly recognised that in addition to developing lumbopelvic stability
and endurance, the optimal approach to training the ‘core’ should also
comprise training to develop different strength qualities (Hibbs et al. 2008).
Furthermore, these stability, endurance and strength qualities are expressed in
a variety of postures and movements. It is logical that these diverse training
goals will require a range of different training methods to be employed during
the course of an athlete’s physical preparation.
Postural stability neuromuscular training
Some authors have questioned the need for dedicated training for the postural
muscles that provide local stability (Willardson 2007), based on the contention
that these muscles will automatically be recruited simultaneously when
athletes perform higher-intensity core exercises and more challenging
exercises in the gym. It has, however, been emphasised that the deep postural
muscles that provide local support and stability must not be neglected when
training to develop athletes’ ‘core’ strength and/or stability in order to avoid a
scenario whereby the larger more superficial muscles attempt to compensate
at the cost of restricted and impaired movement (Hibbs et al. 2008).
It is generally recognised that there is a need for dedicated training to
develop the postural muscles and neuromuscular control capacities involved
with precise control of lumbopelvic posture and maintaining whole-body
equilibrium (Hibbs et al. 2008). This form of training comprises ‘low
threshold’ postural movements that primarily demand endurance and motor
control, which distinguishes this form of training from more intensive core
training that essentially provides a strength challenge (McGill 2010).
As described in a previous section, the cues and techniques that are
employed to help engage the relevant deep postural muscles when performing
this form of training play a decisive role. Specifically, any cues that cause
hollowing of the abdominal wall, which compromises the function of the
more superficial muscles that brace the trunk, should be avoided (McGill
2006c).
‘Low threshold’ core exercises
These training modes comprise the more basic static floor exercises and
exercises typically employed in corrective training and rehabilitation.
Examples include the quadruped or ‘bird-dog’ exercise (McGill 2007b), supine
bridge, and prone hip extension (Lewis et al. 2009). These exercises primarily
focus on the deep lumbar stabilisers and low-intensity exercises for the hip
musculature. Essentially, these exercises can be viewed as a tool to develop
the athlete’s motor control and recruitment of deep postural muscles and
muscles of the hip girdle (Hibbs et al. 2008; McGill 2010). Another objective of
these exercises is to develop proprioception and particularly the ability to
sense lumbar spine positioning and orientation of the pelvis (Carter et al.
2006). The emphasis when performing these exercises is on maintaining a
neutral spine posture and holding the pelvis stable.
The coaching cues employed when athletes perform these exercises appear
to exert a strong influence on patterns of muscle activation and recruitment of
accessory muscles. For example, the timing and degree of gluteal muscle
activation when female subjects were given verbal cues to engage these
muscles prior to performing a prone hip extension exercise were shown to be
significantly different than when these subjects performed the same exercise
without any cues (Lewis and Sahrmann 2009). The ranges of motion employed
when performing these exercises also influence muscle activation and joint
forces incurred (Lewis et al. 2009).
A critical element common to all training modes employed to develop these
capabilities is the inclusion of a static hold during the exercise. This static hold
element has been found to differentiate rehabilitation training modes that
proved successful in developing the deep postural muscles, including
multifidus (Danneels et al. 2001). With respect to repetition schemes, static
hold durations of less than ten seconds are advocated for developing
endurance in a way that avoids the adverse effects of oxygen starvation and
acidosis (McGill 2010). The instruction to take a full breath during these static
hold phases is designed to emphasise maintaining stabiliser muscle activation
in a way that is independent of breathing patterns. The ability to maintain
muscle activation during challenged breathing is a key indicator of effective
versus ineffective stabiliser motor control patterns (McGill 2007a). In addition,
this deep breath facilitates (partial) relaxation of the larger superficial
abdominal muscles (particularly rectus abdominis), which encourages proper
activation of the local lumbar stabilisers and deeper abdominal wall muscles.
One study investigated the acute effects of performing a variety of lowintensity lumbopelvic stability exercises (Crow et al. 2012). The exercises
selected were designed to activate the gluteal muscles, and included the
quadruped, supine bridge and prone single-leg hip extension. These exercises
were completed prior to performing a maximal unloaded jump squat, and
higher power outputs were observed in the elite team sports players studied,
compared to performing either no warm-up or a warm-up on a vibration
platform (Crow et al. 2012). It therefore appears that these exercises might
serve a potentiating effect when employed as part of the warm-up prior to
training and competition.
Postural control and proprioceptive training
The importance of sensorimotor control capacities in relation to core stability
has been highlighted (Borghuis et al. 2008). Accordingly, proprioceptive
training interventions employed in isolation can elicit improvements in
standard measures of core stability and postural control (Romero-Franco et al.
2012). Proprioceptive training modes featuring domed balance training devices
are similarly reported to positively influence lower limb biomechanics and the
associated loading on lower limb joints (Myer et al. 2006a, 2006b). This is
particularly relevant to certain athlete populations, for example female
athletes, who characteristically exhibit suboptimal postural traits during
athletic activities (Mendiguchia et al. 2011).
Some of the exercises involved in developing these elements will have
aspects in common with the training modes described in Chapter 3. In
addition, specific balance and proprioceptive exercises can be employed which
replicate the particular movements involved in the sport. For example, the
implementation of a range of sprinting-specific proprioceptive exercises
incorporating domed balance training devices and Swiss balls has been
described for track sprinters (Romero-Franco et al. 2012). The training
intervention employed was successful in eliciting improvements in measures
of postural sway and control of centre of mass.
Lumbopelvic strength and higher load stability
training modes
During the higher load training modes described in the following sections it is
vital that the deep postural muscles are engaged. Conceptually the deep
postural muscles represent the core of the ‘core’, with the larger muscles and
connective tissues forming the outer layers on top. Much the same cues to
those employed during postural training described above can be used to
engage these muscles, and this will help to ensure pelvis and lumbar spine
alignment is maintained so that the larger muscles of the hip girdle and trunk
are able to function optimally. Co-contraction of these larger muscles acts to
stiffen the torso to help maintain postural integrity under the loading
conditions imposed by the particular exercise (McGill 2010).
The selection of higher load core strength and/or stability exercises should
predominantly be executed with the spine in a neutral position, as opposed to
exercises such as abdominal curls or crunches that involve repeated spine
flexion. Training in a neutral spine/pelvis position better reflects the posture
employed during the majority of speed and change of direction movements
(McGill 2010). Furthermore, this approach also avoids a potential mechanism
for low back pain and injury (McGill 2007b). The cumulative stresses from
performing repetitive spine flexion and extension movements over time can
exceed the failure limits of these tissues (McGill 2010). The significant hip
flexor (for example, psoas) involvement that typically occurs with abdominal
‘curl’ or sit up exercises (Juker et al. 1998) also imposes considerable
compressive loading on the lumbar spine (McGill 2007b). An investigation
into spine loads and trunk muscle activation (that is, injury risk versus
benefit) for a variety of exercises identified the sit up as having the highest
compressive spine load relative to abdominal muscle activation of all the
exercises studied (Axler and McGill 1997).
Static trunk stability exercises
As discussed in the previous section, exercise selection will effectively
comprise progressions and variations of the front plank, bridge and side
bridge exercises. There are numerous means to progress the stabilisation and
strength stimulus with these exercises, with various permutations. For
example, the stability challenge can be increased by incorporating
contralateral limb movement to challenge equilibrium, and/or performing the
exercises on a labile surface (for example, stability ball, domed training
device). Performing a given exercise on a labile (that is, unstable) surface
increases the stability challenge which in turn increases the level of trunk
muscle activity – activation of external obliques in particular has been shown
to be enhanced in the exercises studied (Vera-Garcia et al. 2000). Any
combination of these progressions can be employed in the design of static core
strength and/or stability exercises.
Variations of bridging exercises are widely advocated to develop the
capacity to engage the muscles of the hip girdle whilst concurrently activating
the stabilisers of the trunk (McGill 2006f). The efficacy and importance of the
side bridge exercise has similarly been advocated previously (Gamble 2007a)
based upon EMG data (Behm et al. 2005) and lower back compressive loads
recorded during this exercise (Axler and McGill 1997). Where possible,
exercise selection should favour exercises that report a high level of activation
of a broad range of trunk muscles and relatively low compressive load penalty
on the spine, although inevitably there will be some trade-off between these
two factors.
Figure 8.2 Side bridge on domed device
Hip strengthening exercises
Exercise modes will include modified versions of standard exercises employed
in clinical and rehabilitation settings, such as the supine bridge exercise. For
example, a loaded version of the supine bridge, termed the barbell hip thrust,
has become popular over recent years (Contreras et al. 2011). As well as the
addition of external resistance, modifications associated with eccentric
training approaches might also be considered. One example, using the barbell
loaded bridge exercise, is that the eccentric movement might be performed on
a single leg before returning to two legs for the concentric portion of the
exercise.
Torsional stability training modes
As with the static trunk stability exercises described, exercise selection will
predominantly feature advanced versions of standard exercises (that is, plank,
bridge, side bridge). The front plank in particular is amenable to challenging
torsional stability, which is reflected in its use in movement screens employed
with athletes to assess this capacity (McGill 2006a). The torsional stability
challenge with these exercises is mainly achieved by manipulating the points
of contact – that is, moving from equal weight-bearing to a unilateral base of
support. This can be done in combination with labile supporting surfaces, for
example by employing domed devices or stability balls.
Unilateral resisted training modes
This form of lumbopelvic training comprises alternate limb or single-limb
resisted movements employing cable resistance or free weights, executed in a
weight-bearing posture. Hereby, the athlete is required to maintain postural
integrity under conditions of external loading. These exercises specifically
challenge the ability to brace the trunk and hip girdle in order to maintain a
stationary and stable posture as the athlete performs the resisted movement
with upper or lower limb(s). This form of stabilising challenge therefore
features elements of both torsional stability and isometric trunk and hip
muscle strength.
For example, a variety of upper limb resistance exercises performed in
standing have been investigated as a trunk muscle strength training modality
(Tarnanen et al. 2012). A previous study had noted significant levels of
activation recorded from selected core muscles during alternate limb and
unilateral resistance exercises (Behm et al. 2005). It has, therefore, been
proposed that this approach might offer a superior means to elicit trunk
muscle activation in the range required for gains in strength, in contrast to the
relatively lower muscle-activation levels observed with common floor-based
core stability exercises. In support of this contention, a range of unilateral
cable-resisted upper limb exercises were reported to elicit activation levels
greater than 60 per cent of maximum for selected trunk and back muscles, on
both contralateral and ipsilateral side to the upper limb performing the
resisted movement (Tarnanen et al. 2012).
Figure 8.3 Swiss ball bridge with leg raise
Figure 8.4 Single-leg alternate arm cable press
The importance of movement specificity has been emphasised for this form
of training (Hibbs et al. 2008). Specifically, the recruitment and sequence of
activation of trunk muscles should correspond to what occurs during
movement in the sport. There is a degree of feed-forward control of trunk
muscle activation, corresponding to the anticipated stabilisation challenge
(Hibbs et al. 2008). Accordingly, in order to optimise carry-over of neural
adaptations following training, the design of core strengthening exercises
should aim to reflect the type of loading conditions the player is exposed to
during movements encountered in their sport.
Rotational training
It has been identified that it is important to differentiate between twisting and
twisting torque (McGill 2010). The combination of twisting movements
performed under load can be particularly injurious for the spine. In general,
the safest and best approach may be to separate twisting exercises from
exercises involving rotational torques. Specifically, twisting movements
should be performed under limited load, and performed chiefly by generating
torque from the hips with a neutral and braced spine (McGill 2010).
While it is important to be strong and stable during movements where the
hips and shoulders are aligned, it is equally critical that the athlete is able to
retain lumbopelvic stability and posture when the pelvis and shoulders are
moving independently of each other. This situation occurs not only during the
flight phase when running, but also during the pivoting and twisting
movements involved in change of direction activities. From this point of view,
it would appear vital that exercise selection for stabilisation exercises
progresses to movements where the motion of the shoulders is dissociated
from the hips, and vice versa.
Figure 8.5 Swiss ball Russian twist
Conclusions
A systematic approach to athletic training for the ‘core’ requires that the
strength and conditioning specialist accounts for all the different aspects
described that underpin lumbopelvic stability. For example, low threshold
core stability and postural control exercises should be performed on a daily
basis, alongside a variety of higher load training modes designed to elicit
greater levels of muscle activation and increase core strength. Whereas the
latter core strength exercises can be integrated into the athlete’s strength
training workouts in the weights room, the low-intensity exercises for the
local stabilisers require high degrees of concentration and focused mental
attention. As such they are not amenable to the high levels of activity and
psychological arousal that are characteristic of a weights room setting.
Accordingly, it is recommended that these low-intensity exercises might be
undertaken as a stand-alone session. Alternatively, exercises of this type have
been successfully employed as part of the warm-up or prior to a workout or
other training session.
As with all training, lumbopelvic stability training should incorporate
progression and specificity (Cissik 2002; Stephenson and Swank 2004). In the
case of dynamic lumbopelvic stability training particularly, intensity of
loading and exercise selection should be implemented within the context of
the athlete’s periodised training plan (Stephenson and Swank 2004).
Furthermore, the approach taken should reflect the needs of the individual
athlete, based upon their training and injury history (Stephenson and Swank
2004). This will necessarily include relevant screening or fitness test data –
such as the relationship between flexor, extensor and side bridge test
endurance times (McGill 2004).
Practices on competition day, such as warm-up and athletes’ activity while
waiting to perform, should also not be overlooked as these appear to be key
factors with respect to lumbopelvic function and lumbar spine health. A
particular concern for non-starting players in team sports is the increase in
lumbar spine stiffness observed from sitting on the bench waiting to enter into
the game – reversing any positive effects of pre-match warm-up (Green et al.
2002). As such the musculature that provides lumbopelvic stability should not
be overlooked during warm-up – particularly in the case of non-starting
players.
9
TRAINING FOR INJURY PREVENTION
Identifying risk factors
Introduction
A major application of training for athletic preparation is to help guard
against injury, and ultimately reduce the frequency and severity of injuries
sustained by players in the sport. From this viewpoint one of the positive
outcomes of strength training is increasing the strength and structural
integrity of muscle and bone, and associated connective tissues. This
effectively serves to increase the failure limits of these tissues.
Sport-specific physical conditioning can favourably influence injury risk
when playing team sports. One general protective effect is that appropriately
conditioned players are more resistant to the neuromuscular fatigue that
renders athletes susceptible to injury (Hawkins et al. 2001; Murphy et al. 2003;
Verral et al. 2005). The importance of this is illustrated in the common trend
in many sports for higher injury rates in the latter stages of matches when
players are fatigued (Best et al. 2005; Brooks et al. 2005a; Hawkins and Fuller
1999; Hawkins et al. 2001). Participating in metabolic conditioning appropriate
to the sport serves to help guard against the negative effects of neuromuscular
fatigue (Heidt et al. 2000; Verral et al. 2005).
In addition to these general protective effects of strength training and
metabolic conditioning to raise players’ resistance to the stresses and effects of
fatigue incurred during games, another application of training is to
specifically guard against the particular injuries associated with the sport
(Kraemer and Fleck 2005). Specific neuromuscular and strength training
interventions can be employed to target the particular risk factors and injury
mechanisms associated with a certain type of injury in the sport. Therefore
the logical first step when designing sport-specific injury prevention training
is identifying the injuries that are characteristic of the particular sport and
playing position, and the relevant risk factors associated with these injuries.
Likewise, another relevant consideration is the intrinsic risk factors that might
predispose each individual player to certain injuries.
Injury risk factors for team sports players
Injury risk can be stratified into intrinsic risk factors associated with the
individual player and extrinsic risk factors that concern the environment in
which the player trains and competes (Arnason et al. 2004; Quarrie et al.
2001). A logical first step in designing injury prevention programmes is to
identify both the intrinsic risk factors specific to the individual player and the
extrinsic factors associated with competing in the sport (Murphy et al. 2003).
Once predisposing factors and typical mechanisms for injury are identified,
specific preventative measures can then be taken in order to address these
intrinsic and extrinsic risk factors (Arnason et al. 2004; Bahr and Krosshaug
2005).
Intrinsic injury risk factors
Profiling each individual player in the team offers a means to identify
intrinsic risk factors. Relevant information will include age, ethnicity, gender,
anthropometric characteristics, medical history (including previous and
current injury status), training status and a musculoskeletal assessment that
includes dynamic tests of mobility and stability. For example, age can be a
predictor of general injury risk (Murphy et al. 2003) – older players were
reported to suffer higher frequency of injuries in a cohort of senior soccer
players in Iceland (Arnason et al. 2004). Players of black ethnic origin are
identified as being more prone to certain muscle injuries – particularly
hamstring muscle strains (Woods et al. 2004). Team sports players with high
body mass index are shown to be at greater risk for certain injuries, such as
non-contact ankle sprains (McHugh et al. 2006).
Gender is a major intrinsic risk factor for team sports injuries: female
players sustain a significantly greater number of lower limb injuries (Murphy
et al. 2003). This female gender risk factor is particularly evident for knee
injury – females are two to ten times more likely to suffer ACL injury when
participating in sport (Silvers and Mandelbaum 2007). Examination of NCAA
injury data shows that the rate of ACL injury among female collegiate soccer
and basketball players has remained constant (and consistently higher than
males) over recent years, whereas rates of ACL injury in male collegiate
soccer have declined over the same period 1990–2002 (Agel et al. 2005). This
phenomenon of higher injury rates among female players endures despite
considerable research attention and numerous injury prevention strategies
designed to address the heightened risk of knee injury among female athletes.
Previous injury is identified as a key intrinsic risk factor that predisposes
players to subsequent injury (Meeuwisse et al. 2003; Murphy et al. 2003;
Quarrie et al. 2001). For example, senior soccer players who reported previous
injuries were found to be four to seven times more likely to suffer injury –
particularly repeat incidence of a prior injury (Arnason et al. 2004).
Inadequate rehabilitation and premature return to play following injury are
similarly identified as intrinsic risk factors (Murphy et al. 2003). The
consequences of re-injury also tend to be more severe in terms of days lost
post-injury in comparison to new injuries (Brooks et al. 2005a, 2005b).
Individual screening and functional assessment can identify intrinsic
musculoskeletal risk factors (musculoskeletal and movement screening is
covered in more detail in Chapter 2). Measures of joint laxity are associated
with injury risk – higher levels of laxity indicative of mechanical instability
are linked to increased injury incidence (Murphy et al. 2003). Muscle
flexibility scores represent another intrinsic injury risk factor. The average
preseason hamstring and quadriceps flexibility scores of soccer players who
went on to sustain hamstring and quadriceps injury during the season were
lower than those who remained injury-free (Witvrouw et al. 2003). A similar
association between decreased scores on hip range of motion and subsequent
incidence of adductor muscle strains in soccer players is also reported
(Arnason et al. 2004). Imbalances in measures of strength and flexibility are
also suggested to be associated with injury risk (Knapik et al. 1991).
Extrinsic injury risk factors
Environment-related extrinsic risk factors concern the characteristic demands
of the sport and associated training, level of competition, equipment,
environmental conditions and the playing surface. The prevalence of certain
types of injury tends to be characteristic of the particular sport. Players are
also more likely to suffer injury during games than during practice (Murphy
et al. 2003). Higher grades of competition within a particular sport are
typically associated with greater incidence of injury in general, and also with
more frequent occurrence of specific injuries – such as anterior cruciate
ligament (ACL) injury (Orchard et al. 2001).
Errors in training design and implementation also represent major extrinsic
injury risk factors. For example, poor lifting technique and incorrect
movement mechanics that expose musculoskeletal structures to excessive
strain can be caused by inappropriate instruction and poor coaching. Similar
training errors include poor strength-training design that creates muscle
imbalances or exacerbates pre-existing ones. Likewise, programming errors
that impose excessive loading in terms of frequency or training volume can
lead to nonfunctional overreaching which predisposes a player to overuse
injury and injury due to residual neuromuscular fatigue.
Playing equipment may have a positive impact in terms of reducing contact
injuries or a negative impact. Negative examples include football shoes that
increase the traction between the shoe and playing surface in a way that
resulted in a rise in ACL injuries (Lambson et al. 1996) and basketball shoes
with air cells in the heel that were associated with four times greater
incidence of ankle injuries, presumably by decreasing rearfoot stability
(McKay et al. 2001). Positive examples include the introduction of mandatory
full face masks in collegiate ice hockey that has served to dramatically reduce
facial and dental injuries (Flik et al. 2005). Paradoxically, protective equipment
may also lead to more aggressive play and risk-taking, which can in fact cause
an increased number of injuries (Bahr and Krosshaug 2005). The interaction
between environmental conditions and the playing surface is an important
factor from an injury risk viewpoint – particularly with respect to the effect of
weather conditions on resistance between the playing surface and the sports
shoe (Orchard et al. 2001).
Epidemiological studies reporting injury data for representative groups
participating in a particular team sport offer a means to help identify the
extrinsic risk factors associated with the sport. Participation in a team sport
involves inherent risk that may also vary for different playing positions; in
turn this will tend to be reflected in the particular injuries reported. Injury
surveillance data therefore provides a useful source of information about the
relative incidence of different types and sites of injury in the sport. Such data
may also offer further insight into specific risks associated with different
playing positions, relative risk of injury during training versus competition,
and the frequency and types of injury common to different phases of play
(Shankar et al. 2007).
Representative injury data for selected team sports
Baseball
The majority of injuries associated with baseball concern the shoulder
complex; the typical injury mechanism is linked to repetitively performing the
throwing motion during practices and games. Common injuries reported
involve the rotator cuff musculature, and onset is typically relatively insidious
– hence most are classed as overuse injuries (Mullaney et al. 2005). An
apparent critical factor with respect to incidence of shoulder impingement
injury is that there is appropriate balance between those muscles that act to
hold the head of the humerus in the shoulder socket and the muscles that
accelerate the throwing arm.
Potential for damage would appear to be increased by deterioration of
sound throwing technique due to the effects of fatigue. That said, pitchers
were found to be quite resistant to fatigue-related changes in pitching
kinematics and kinetics during a simulated game under controlled conditions
(Escamilla et al. 2007). A study assessing muscular fatigue reported that the
collegiate and minor league pitchers examined were similarly resilient on a
variety of upper and lower limb strength-test measures with modest, albeit
statistically significant, differences between pre-game and post-game force
output scores (Mullaney et al. 2005). The lack of significant reduction in force
output scores of the external rotator musculature found in this study may,
however, have been a consequence of the fact that they contract in an
eccentric fashion during the pitching action; force output tends to be much
better maintained with repeated eccentric muscle contractions.
Similarly, issues associated with the relative timing of hip, trunk and
shoulder rotation during the throwing action have also been identified as
potential causative factors for shoulder and upper limb pain and injury in
baseball (Aguinaldo et al. 2007). Specifically, the magnitude and sequential
timing of rotation between hip, trunk and shoulder determines how angular
momentum is transferred from these segments to the shoulder and distal
upper limb joints. If the timing of this sequential motion is not optimal, there
will be a loss of angular momentum for which the player must compensate by
generating greater torques at the shoulder and upper limb in order to
maintain throwing velocity (Aguinaldo et al. 2007). This scenario is suggested
to influence the incidence of shoulder and elbow pain and injury, particularly
among less skilled players, as greater torques generated at the upper limb
joints will place increased strain upon these joints and connective tissue
structures. One study identified that the relative timing of trunk rotation in
the pitching action differentiated professional players from pitchers at college,
high school and youth level (Aguinaldo et al. 2007). Professional players were
found to initiate trunk rotation much later in the pitching cycle, and in turn
these players reported lower internal rotation torques at the pitching shoulder
in comparison to college and high school players.
Baseball pitchers often exhibit altered range of motion and strength ratios
on their dominant (throwing arm) side compared to their non-dominant side.
Specifically, a common finding is reduced range of motion in internal rotation
accompanied with increased external rotation on the dominant versus nondominant side (Mullaney et al. 2005). These changes in flexibility are mirrored
by adaptations in muscular strength for these opposing movements. Pitchers
commonly achieve higher force output in internal rotation but exhibit
compromised external rotation force measured on their throwing arm in
comparison to the contralateral side (Mullaney et al. 2005). Similarly,
compromised strength scores are reported for specific tests of rotator cuff
muscle strength – specifically supraspinatus – in these players.
A common complaint among young baseball players concerns damage to
the epiphyseal cartilage at the head of the humerus (Sabick et al. 2005). A
condition called ‘Little League shoulder’, or sometimes termed humeral
epiphysiolysis, is prevalent among young pitchers – essentially arising from
repeated trauma to the growth plate at the neck of the humerus. Key factors in
the incidence of this injury appear to be the combination of high rotational
stresses and distraction forces during the throwing action, and weakness of
the developing musculoskeletal system (Sabick et al. 2005). It has been
suggested that it is the torsional forces during throwing in particular which
are likely to be the major cause of damage to the epiphysis, given that growth
plates are less resilient to this type of loading.
Soccer
Available data indicate that an elite male soccer player can expect to sustain
one performance-limiting injury each season (Junge and Dvorak 2004). Senior
players competing in the top two divisions in Iceland were reported to sustain
24.6 injuries per 1,000 player hours during matches and 2.1 injuries per 1,000
hours in training (Arnason et al. 2004). A study of four English professional
soccer clubs reported injury incidence of 27.7 injuries per 1,000 player hours
during matches and 3.4 injuries per 1,000 player hours for training (Hawkins
and Fuller 1999). The incidence of injury during both matches and training
among youth players at the same English professional clubs was markedly
higher – 37.2 and 4.1 injuries/1,000 player hours for matches and training
respectively (Hawkins and Fuller 1999).
Injuries commonly reported in soccer are lower limb – typically involving
ankle and knee joints, and the thigh and calf musculature (Junge and Dvorak
2004). Lower limb injuries comprised 82 per cent of all injuries during a season
of competition in the senior elite leagues in Iceland (Arnason et al. 2004) and
87 per cent of all injuries in English professional soccer (Hawkins et al. 2001).
In an earlier study of English professional soccer the most common sites of
lower limb injuries were the thigh (23 per cent of total), ankle (17 per cent),
knee (14 per cent) and lower leg (13 per cent) (Hawkins and Fuller 1999). The
majority of injuries observed were muscle strains (41 per cent of total
injuries); sprains (20 per cent) and contusions (20 per cent) were the next most
common types of injury.
A high incidence of muscle strains is reported in soccer: 8.4 injuries per
1,000 match hours and 0.8 injuries per 1,000 training hours were recorded
during a season of competition at elite senior level in Iceland (Arnason et al.
2004). Due to the demands of the sport, soccer players are at particular risk for
both hamstring (Verral et al. 2005) and adductor muscle injuries (Arnason et
al. 2004; Nicholas and Tyler 2002). Joint and ligament sprains are likewise
relatively common: reported at 5.5 injuries per 1,000 match hours and 0.4
injuries per 1,000 training hours in Icelandic senior elite soccer, most
involving knee or ankle (Arnason et al. 2004). Over three-quarters of knee
ligament injuries recorded in English professional soccer were to the medial
collateral ligament (MCL) (Hawkins and Fuller 1999; Hawkins et al. 2001).
However, severe knee ligament injuries in soccer most often involve the
anterior cruciate ligament (ACL) (Arnason et al. 2004; Hawkins and Fuller
1999).
On average, injuries reported in English professional soccer resulted in 24.2
days lost to training and competition (Hawkins et al. 2001). Around a third of
injuries reportedly result from bodily contact with another player (Junge and
Dvorak 2004) – player contact was identified in 41 per cent of all injuries in
English professional soccer (Hawkins and Fuller 1999). Both senior
professionals and youth players are also reported to sustain more injuries to
their dominant leg – reflecting players’ greater use of their dominant leg
when tackling and being tackled (Hawkins and Fuller 1999; Hawkins et al.
2001). Non-contact injuries are typically incurred when running or changing
direction.
Studies of soccer players typically report a high incidence of re-injury;
repeat injuries make up between a fifth and a quarter of all injuries sustained
(Hawkins and Fuller 1999; Junge and Dvorak 2004). Such findings indicate that
previous injury is a major risk factor for subsequent injury in soccer (Arnason
et al. 2004). The severity of re-injuries with respect to time lost also tends to
be greater than with the original injury (Hawkins et al. 2001). There is
therefore a suggestion that rehabilitation undertaken in elite-level soccer –
particularly following ankle sprains and posterior thigh strains – is
insufficient or incomplete (Hawkins and Fuller 1999; Junge and Dvorak 2004).
Training injuries in English professional soccer appear to peak in July,
coinciding with the end of pre-season training, whereas match injuries show a
peak at the start of the playing season in August (Hawkins et al. 2001). This
has led to suggestions that the content and effectiveness of pre-season
physical preparation and adherence to off-season maintenance training may
be inadequate. Conversely, the number of injuries among youth players also
tends to rise towards the end of the playing season (Hawkins and Fuller 1999).
In this case, cumulative fatigue associated with the burden of a large number
of matches may play a role in the injury patterns observed with these young
players.
Depending on the injury definition, overall injury rates for elite senior
female soccer players appear to be similar to the corresponding data reported
for males. Rates of ‘traumatic’ (as opposed to overuse) injury reported during
matches in the German national league were 23.3 per 1,000 player hours
during matches and 2.8 per 1,000 player hours during training (Faude et al.
2005). Reported match and training injury incidence among professional
female soccer players in the United States were lower, possibly due to the
different methods used in collecting injury data (Giza et al. 2005). The
majority of injuries reported in elite senior women’s soccer are lower limb –
comprising between 60 per cent (Giza et al. 2005) and 80 per cent of total
injuries (Faude et al. 2005). A study of female high school soccer players in the
United States reported that all injuries sustained by 300 participating players
(ages 14–18 years) during a season of play were to the lower limb (Heidt et al.
2000).
For the most part, injuries sustained by female soccer players appear evenly
distributed between thigh, knee and ankle (Faude et al. 2005); however, a
study of professional women’s soccer in the United States has reported a
relatively large number of head and/or facial injuries (Giza et al. 2005).
Another study indicated that female soccer players may be prone to lower
back injury (Nadler et al. 2002). This is supported by the surprisingly large
number of back injuries reported by female players in the German national
league (Faude et al. 2005). Women’s soccer appears to involve a higher
number of (lower limb) joint and/or ligament sprains but a lower proportion
of muscle strains in comparison to men’s soccer (Faude et al. 2005; Giza et al.
2005).
Another apparent difference is that injuries sustained by female soccer
players are also more likely to be severe (Heidt et al. 2000). Of particular
concern is the high incidence of ACL injury among female soccer players,
especially during matches – reported to be in the region of 0.90 (Giza et al.
2005) to 2.2 ACL injuries per 1,000 player match hours (Faude et al. 2005) in
elite senior women’s soccer. A review of NCAA injury data also revealed that
female collegiate soccer players sustained significantly more ACL injuries
than male collegiate soccer players (Agel et al. 2005). Furthermore, a greater
proportion of these ACL injuries sustained by female collegiate soccer players
resulted from non-contact mechanisms compared to the corresponding data
for male players.
Volleyball
The incidence of injury in volleyball is estimated at 4.1 injuries per 1,000
player hours during matches and 1.8 per 1,000 player hours during training
(Verhagen et al. 2004). The majority of acute injuries reported in volleyball
involve the lower limb and the most common type of injury is ligament strain.
Ankle was the reported site of injury comprising 41 out of the 100 injuries
reported in male and female volleyball players during the course of a season
in Holland (Verhagen et al. 2004) – ankle inversion sprains in particular are
very common (Stasinopoulos 2004). Nearly two-thirds of ankle sprains
reportedly occur when players are at the net, sometimes due to contact with
team-mates or opponents upon landing (Verhagen et al. 2004).
In contrast to the data for men’s volleyball, female volleyball players appear
to suffer a similar number of injuries during practice and competition. Injury
rates during NCAA competition in the United States, although slightly greater
(4.58 per 1,000 exposures), were not markedly higher than those during
practice (4.1 injuries per 1,000 exposures) (Agel et al. 2007c). Ankle ligament
sprains comprised 44.1 per cent of game injuries and 29.4 per cent of injuries
during practice; the greater number of ankle injuries in games is partly due to
the larger proportion of ankle injuries involving player contact during
competition versus practice. Shoulder injuries are also quite commonly
reported during games and practices in women’s volleyball – particularly
muscle and/or tendon strain injury (Agel et al. 2007c).
There appears to be a particular risk of re-injury following ankle sprains in
volleyball (Verhagen et al. 2004) – a quarter of players reporting ankle injury
had sustained an ankle injury during the preceding twelve months. Volleyball
is also associated with particular overuse injuries most often involving the
shoulder or lower back, with knee injuries being the third most common
overuse injury reported by volleyball players (Verhagen et al. 2004).
Elite volleyball players appear to exhibit various musculoskeletal issues
associated with the shoulder on their dominant side, which are identified as
risk factors for overuse shoulder injury (Wang and Cochrane 2001). A study of
elite volleyball players reported high incidence of a range of disorders,
including: (dominant versus non-dominant side) muscular imbalance;
restricted shoulder mobility; impaired eccentric strength; relative weakness in
external rotation; and scapular asymmetry. Of these conditions, the imbalance
between concentric internal rotator muscle strength and eccentric external
rotator strength on the dominant side was shown to be significantly related
with reported incidence of shoulder injury and pain in elite English volleyball
players (Wang and Cochrane 2001).
Another reportedly common condition among volleyball players is patellar
tendinosis – a knee joint extensor overuse injury more commonly known as
‘jumper’s knee’ (Gisslen et al. 2005). The incidence of this overuse injury is
likely to be underestimated by injury surveillance studies, as players will tend
to continue to play matches despite experiencing pain (Verhagen et al. 2004).
‘Jumper’s knee’ afflicts a large proportion of volleyball players over the course
of their career and is even reported to be quite prevalent among elite junior
players (Gisslen et al. 2005).
Basketball
A study of injury surveillance data from collegiate basketball in the United
States reported the incidence of injuries during games to be 9.9 injuries per
1,000 athlete exposures during NCAA competition (Dick et al. 2007b). This is
markedly higher than a study of men’s intercollegiate basketball in Canada,
which reported an overall injury rate of 4.94 injuries per 1,000 athlete
exposures (Meeuwisse et al. 2003). This latter study also noted that injury
rates for minor injuries (causing less than seven sessions to be missed) were
similar between games and practices in Canadian collegiate competition, but
the incidence of more severe injuries was 3.7 times higher during games than
during practice. The rates of injury reported during practices in NCAA
competition is 4.3 per 1,000 athlete exposures (Dick et al. 2007b).
The majority of injuries reported in NCAA men’s basketball involved the
lower limb, with ankle ligament sprains comprising 26.2 per cent of game
injuries and 26.8 per cent of practice injuries (Dick et al. 2007b). The ankle was
also the most frequently reported site of injuries in Canadian collegiate
basketball but injuries to the knee resulted in the most time out of
participation (Meeuwisse et al. 2003). Knee injuries similarly made up a
substantial number of injuries (approximately 10 per cent of all game and
practice injuries) reported in NCAA basketball – most commonly ‘internal
knee derangement’ (ligament and/or cartilage injury) or patellar injuries (Dick
et al. 2007b). Although not generally classed as a contact sport, a third of the
injuries reported in Canadian intercollegiate basketball resulted from contact
with another player (Meeuwisse et al. 2003). That said, ACL injuries in men’s
intercollegiate basketball are more commonly non-contact (Agel et al. 2005,
Dick et al. 2007b). Most injuries were reported to occur in the ‘key’ area of the
court and of all the playing positions the most injuries were recorded by
centres (Meeuwisse et al. 2003).
The reported rate of injury during matches in women’s collegiate basketball
in the United States was 7.68 injuries per 1,000 athlete exposures (Agel et al.
2007b). This value appears to be lower (3.66 injuries per 1,000 athlete
exposures during games) among female players competing at high school level
(Borowski et al. 2008). The majority of injuries in women’s basketball involve
the lower limb, representing over 60 per cent of all injuries sustained in
women’s collegiate basketball in the United States (Agel et al. 2007b). A study
of high school basketball reported that 35.9 per cent of injuries sustained by
female players involved the ankle and/or foot region, and the knee (18.2 per
cent of all injuries) was the second most common site of injury (Borowski et
al. 2008). An earlier study reported that the lower back is the third most
prevalent site of injury in women’s basketball (Nadler et al. 2002). More recent
injury reporting studies from women’s collegiate and high school basketball in
the United States reported the head and/or face to be the third most prevalent
site of injury (Agel et al. 2007b, Borowski et al. 2008).
The most reported single injury in women’s basketball at high school level
is knee ligament sprain (Borowski et al. 2008). At collegiate level, knee
‘internal derangement’ injury is the second most reported injury in both
games and practices (ankle ligament injury is the most common) (Agel et al.
2007b). In women’s basketball knee injuries were reported to comprise up to
91 per cent of season-ending injuries (Ford et al. 2003). NCAA injury data
spanning 1990–2002 report that the rate of ACL injury was significantly
higher for female collegiate basketball players than males (Agel et al. 2005).
The majority (ranging from 64.3 per cent–89.7 per cent of total depending on
the year) of ACL injuries sustained by female collegiate players were the
result of non-contact mechanisms. The pattern of ankle injuries monitored
during a playing season in female professional basketball peaked during the
initial two months (particularly the first month) following the start of the
season (Kofotolis and Kellis 2007). This would appear to indicate inadequate
or inappropriate physical preparation of players during pre-season.
A high proportion of injuries in female basketball involve player-to-player
contact, representing 46 per cent of all injuries sustained during games of
female collegiate basketball in the United States (Agel et al. 2007b). Similarly,
a study of Greek female professional basketball in Europe identified that the
majority of ankle sprains during matches occurred within the ‘key’ area of the
court (that is, the scoring zone in front of the posts) (Kofotolis and Kellis
2007). This was attributed to the greater number of ankle sprain injuries
involving player-to-player contact within these areas. In accordance with this,
the playing positions which most frequently engage in contesting possession
within the ‘key’ area of the court were also reported to suffer the highest
incidence of ankle injury in female professional basketball in Europe
(Kofotolis and Kellis 2007).
Netball
There is a paucity of published studies documenting injury incidence in
netball, particularly at elite level (Gamble 2011). Based upon the available
studies, the majority of injuries in netball involve the lower limb (McManus et
al. 2006) and the predominant type of injury is ligament sprain or disruption
(Hume and Steele 2000; Stevenson et al. 2000). The majority of injuries are
sustained during competitive matches rather than practices (Saunders and
Otago 2009). The ankle is the most frequent reported site of injury for both
recreational and elite players, followed by the knee (McManus et al. 2006;
Saunders and Otago 2009). In particular, lateral ankle sprain has previously
been identified as the single injury most commonly reported in netball
(Hopper et al. 1999). This injury in netball is typically associated with landing
in a plantar-flexed foot position, combined with forced inversion upon
landing.
Ankle injuries sustained in netball are reported to be frequently associated
with landing and also player-to-player contact (Hume and Steele 2000;
Saunders and Otago 2009). The prevalence of ankle injuries in netball (Hopper
et al. 1999) combined with the high rate of recurrence with this injury
(Swenson et al. 2009) may predispose netball players to the syndrome known
as ‘chronic ankle instability’ (Holmes and Delahunt 2009). A study of netball
indicated almost half of injuries sustained by players during state
championships were recurrences of previous injuries (Hume and Steele 2000).
American football
A recent and comprehensive injury surveillance study for American football
reported an injury rate in high school and college football in the United States
that is almost twice that of basketball (the second most popular sport among
males in these age groups) (Shankar et al. 2007). This was supported by injury
surveillance data from NCAA competition in the United States which reported
36 injuries per 1,000 athlete exposures for games – three and a half times the
rate reported for NCAA men’s basketball (Dick et al. 2007a). There was a
greater relative injury incidence overall for collegiate versus high school
football (Shankar et al. 2007). Unsurprisingly a high incidence of contact
injuries is reported – the majority being sustained when tackling or being
tackled (Shankar et al. 2007).
The sites and types of injury appear to be broadly similar between high
school and collegiate football. One study reported injuries to the knee (16.4 per
cent of all injuries) were most common in collegiate football, followed by the
shoulder (13.2 per cent of total) and then ankle (12.7 per cent) (Shankar et al.
2007). NCAA data indicated a similar pattern; however, the ankle ranked as
the second most common site of game injuries (Dick et al. 2007a). In high
school football, knee (15.2 per cent of all injuries) and ankle (also 15.2 per cent
of total) were the most frequent sites of injury, followed by the shoulder (12.4
per cent of total injuries). Concussions made up a significant number of game
injuries in NCAA men’s football (Dick et al. 2007a). There is similarly a high
reported incidence of concussions in high school football (Shankar et al. 2007).
Competitive play accounts for a considerably higher rate of injury than
practice sessions at both high school (c. four times greater injury rate) and
collegiate level (nearly eight times higher) (Shankar et al. 2007). The injury
rate during practices for NCAA players was reported to be approximately 4
injuries per 1,000 athlete exposures for practice in the fall (autumn), whereas
during spring practice the rate was appreciably higher – approximately 10
injuries per 1,000 athlete exposures (Dick et al. 2007a). During games there are
a lower proportion of muscle and/or tendon strains (high school: 10 per cent
during games versus 24 per cent during practices; college: 14 per cent games
versus 25 per cent practices) (Shankar et al. 2007). Conversely, a higher
proportion of ligament sprains is reported during competitive play (high
school: 33 per cent during games versus 29 per cent practices; college: 39 per
cent games versus 25 per cent practices) (Shankar et al. 2007).
Most injuries during practices are ligament sprains and muscle and/or
tendon strains, which jointly comprised 53 per cent of reported practice
injuries in high school football and 50 per cent of total collegiate football
practice injuries (Shankar et al. 2007). Injuries during practices in high school
football are less severe, with a faster return to play than those sustained
during competition. It has been identified that practices during the spring
season have a two- or three-fold higher injury rate in collegiate football (Dick
et al. 2007a), with a particular increase in the number in severe injuries
(Albright et al. 2004). This appears to be a consequence of players striving to
compete for selection for the upcoming fall (autumn) season. The same study
noted that of all strings of players (in terms of ranking order for selection) the
‘non-players’ (those rated as unlikely to be selected) sustained by far the
greatest number of injuries during practices (Albright et al. 2004). This is
likely a reflection of their typical role as ‘cannon fodder’ during practices.
For both high school and collegiate football, running plays are reported to
account for the greatest number of injuries during games (Shankar et al. 2007).
Running plays are also reported to result in more severe injuries, with the
greatest number of season-ending injuries occurring during running plays. In
keeping with this, the most frequently injured playing positions reported in
high school football are offensive linemen and running backs, and linebackers
are the most injured defensive positions (Shankar et al. 2007). At collegiate
level, although these playing positions continue to be among the most injured
positions, wide receivers also have a similarly high incidence of injury (12.3
per cent of total injuries) to running backs (12.1 per cent of total). Regardless
of playing level, running backs reported the highest incidence of ankle injury
of any playing position (Shankar et al. 2007). The data for match injuries
indicate that passing plays most commonly result in injuries to wide receivers
(offence) and cornerbacks (defence) – unsurprising given the high
involvement of these playing positions in such plays (Shankar et al. 2007).
Rugby union football
Due to the contact nature of the sport, rugby union football has a high
reported incidence of injury. Risk of injury also appears to increase as players
progress towards higher levels of competition (Quarrie et al. 2001). The most
extensive epidemiological study to date in professional rugby union was
undertaken in the United Kingdom, with full participation of all English
Premiership clubs over two seasons (Brooks et al. 2005a). Overall incidence of
injury during domestic matches was reported to be 91 injuries per 1,000
player-hours – considerably higher than is reported for other professional
team sports. Incidence of injury reported at international level is higher still –
97.9 per 1,000 player-hours during the 2003 World Cup competition (Best et al.
2005).
Perhaps unsurprisingly, contact injuries comprise the majority of injuries
recorded during match-play (72 per cent) in professional rugby union (Brooks
et al. 2005a). This is similar to findings reported in elite junior rugby union in
Australia (McManus and Cross 2004). Forward positions (responsible for
contesting possession) have a higher incidence of contact injuries due to their
involvement in set-piece phases (scrum, line-out and kick-off). Similarly,
forwards sustain a higher number of contact injuries when contesting
possession at rucks or mauls, whereas contact injuries sustained by the back
positions are more typically ‘tackle injuries’ – that is, occurring when tackling
or being tackled (Brooks et al. 2005a). As a group, backs are reported to
sustain a greater number of non-contact injuries during domestic senior
professional matches – this was also reported to be the case in elite junior
rugby union in Australia (McManus and Cross 2004).
The lower limb is the most frequent site of injury in rugby union football
and the most frequent reported lower limb injury in professional domestic
rugby is thigh haematoma (Brooks et al. 2005a), albeit the severity of such
injuries was typically minor in terms of time lost. Hamstring injuries were the
second most common injury during matches, reflecting their high incidence
among players in the back positions. Knee injuries represent the most costly
injuries in professional rugby union: the moderately high incidence of knee
injuries combined with their high average severity accounts for the fact that
these injuries result in the greatest number of days’ absence from training and
competition of any injury type (Brooks et al. 2005a; Dallalana et al. 2007). A
high proportion of knee injuries reported in matches (72 per cent) are
sustained during contact (Dallalana et al. 2007). Tackle situations –
particularly being tackled – account for a large number of the ACL (72 per
cent) and MCL (46 per cent) injuries that occur during matches. Shoulder
injuries have the second highest average severity in terms of days absence per
injury (Brooks et al. 2005a) – reflecting that this is the typical site of impact
when tackling opposing players (Gamble 2004b).
The different playing positions in rugby union have designated and quite
specialised roles during play, and as such there is a greater distinction
between positions – for example in comparison to rugby league (Gamble
2004b). This is reflected in marked differences between individual playing
positions in terms of type, incidence and severity of injury sustained during
matches (Brooks et al. 2005a). For example, fly half (back) and hooker
(forward) positions reported the highest frequency of injury during domestic
professional matches, whereas the most severe injuries tended to involve right
locks and open-side flankers (forwards). Overall, the playing positions at most
risk (in terms of both frequency and severity of injury reported) appear to be
hooker (forward) and outside centre (back) in these domestic professional
games. Data from international (2003 World Cup) competition indicated
injury rates were highest for Number 8, open-side flanker (forwards) and
outside centre (back) positions (Best et al. 2005). Similarly, the Number 8 and
flanker positions were found to be the playing positions most at risk of injury
in an elite junior rugby union squad competing in the Australian National
Championships (McManus and Cross 2004).
Unsurprisingly, there is a much lower relative incidence of injury reported
in professional rugby union during training – regardless of the type of
training (Brooks et al. 2005b). Conversely, the severity of training injuries in
terms of days lost is greater than that for injuries sustained during matches.
The majority of training injuries reported are lower limb and mainly comprise
either muscle and/or tendon strains or ligament sprains. Contact skills
practices involve the highest injury rate; however, running conditioning also
accounts for a large proportion of training injuries and non-contact injuries
comprise a higher percentage (57 per cent) of the total training injuries
reported (Brooks et al. 2005b). Strength training shows the lowest injury rates
of all training modes, albeit the greater number of lumbar disc and/or nerve
root injuries reported by forwards (as compared to backs) are attributed to
strength training (Brooks et al. 2005b).
Rugby league football
As is the case with rugby union, the majority of injuries sustained during
matches in rugby league football are tackle injuries (Gabbett 2004). The act of
being tackled in particular is a leading cause of injury in senior professional
rugby league, as it is in rugby union. At amateur level, tackling (as opposed to
being tackled) appears to account for a greater proportion of the total injuries
during matches – possibly due to lower levels of defensive skills (Gabbett
2004).
Another finding in common with rugby union is that injury rates in rugby
league increase at higher levels of competition (Gabbett 2004). The head and
neck are the most common sites of injury reported during matches among
rugby league players (Gabbett 2004). Muscular injuries are the most common
types of injuries during rugby league matches at all levels of competition.
Rugby league football has a lesser emphasis on set-piece phases of play and
possession is not contested after each tackle is made; consequently playing
positions in rugby league are more homogeneous in comparison to rugby
union. Even so, as a group the forward positions tend to make and receive
more tackles during a match and this is reflected in higher overall incidence of
injury among forwards compared to backs at all levels of competition
(Gabbett 2004).
Rugby league football studies also report that injury rates during training
are much lower than in matches (Gabbett 2004). The majority of reported
training injuries sustained by rugby league players are lower limb, with most
being muscle strains. This mirrors the findings reported in professional rugby
union football. A study of rugby league players showed that the use of skillbased conditioning games may reduce the incidence of training injuries
during conditioning activities – in comparison to traditional running-based
conditioning without any game skills element (Gabbett 2002).
Australian rules football
A study of the Australian Football League over three seasons (1997–2000)
reported that the incidence of new injuries during matches was 25.7 injuries
per 1,000 player hours (Orchard and Seward 2002). There was also a high
reported frequency of recurrence of previous injuries. The thigh was the most
frequently reported site of injury in the Australian Football League; the most
common injury type being muscle strains (Orchard and Seward 2002).
Hamstring muscle injuries are a particular concern for the sport (Verral et al.
2005), especially given the very high (34 per cent) recurrence rate reported for
this injury as compared to the 17 per cent overall recurrence rate for all
injuries in this study.
Following hamstring muscle strains, ACL ligament sprains are the next
most prevalent injury reported in the Australian Football League – the
majority of which are attributed to a non-contact mechanism (Orchard and
Seward 2002). The relative incidence of complete ACL tears during matches in
the Australian Football League was reported to be 0.82 ACL injuries per 1,000
player-match exposures and 0.62 injuries per 1,000 player-match exposures for
non-contact ACL tears specifically (Orchard et al. 2001). A history of ACL
reconstruction was identified as a significant intrinsic risk factor for these
injuries in Australian rules football players. Extrinsic risk factors identified as
affecting ACL injury incidence in Australian Football League matches
included weather conditions over the period preceding a game. Specifically,
28-day evaporation values and rainfall over the year prior to the game were
identified as influencing frequency of ACL tears – likely due to the associated
impact upon shoe-playing surface traction when there were particularly dry
pitch conditions (Orchard et al. 2001).
Ice hockey
A study of Division One collegiate men’s ice hockey in the United States
reported injury rates during matches as 13.8 per 1,000 player exposures and 2.2
per 1,000 player exposures during practice (Flik et al. 2005). The majority of
injuries reported were attributed to contact – occurring during collisions with
opponents (32.8 per cent of all injuries) or the perimeter boards surrounding
the playing area (18.6 per cent of total injuries). The most common sites of
injuries reported with these players were knee and/or leg (22 per cent of total),
head (19 per cent of total), and shoulder (15 per cent) (Flik et al. 2005).
Concussion was the single most frequently reported injury in American
collegiate men’s ice hockey – representing 18.6 per cent of all reported injuries
– the majority of which occurred during competitive matches (Flik et al. 2005).
Illegal activity – specifically elbowing – was identified as being the cause of
many concussions during games. Forwards sustained the most concussions –
suffering twice the number of concussion injuries reported by defensemen
(Flik et al. 2005). MCL strains were the second most frequently reported injury
in the study – all of them occurring during games. Another frequently
reported injury that is particularly severe in terms of time lost is syndesmotic
or ‘high ankle’ sprain – an injury that appears to be much more common in
ice hockey than other sports. This reported incidence of ankle syndesmotic
sprain injury appears fairly evenly distributed between games and practices
(Flik et al. 2005).
It has been reported that overall injury incidence did not appear to differ
significantly between collegiate men’s and women’s ice hockey in Canada
(Schick and Meeuwisse 2003). However, the women’s collegiate ice hockey
players featured in the study had played far fewer games. When match data
were compared, injury rates were significantly higher: 22.4 injuries per 1,000
match exposures for men versus 10.43 injuries per 1,000 match exposures for
female collegiate ice hockey players (Schick and Meeuwisse 2003). Injury
surveillance data over four seasons following the start of NCAA women’s ice
hockey competition in the United States in 2001 reported 12.6 injuries per
1,000 athlete exposures in games, compared to 2.5 injuries per 1,000 athlete
exposures during practices (Agel et al. 2007b). These data are broadly similar
to the injury data previously reported for women’s collegiate competition in
Canada (Schick and Meeuwisse 2003).
Female ice hockey has key differences in the playing rules: games are
shorter in length and the rules prohibit intentional body checking. Despite
this, the vast majority of injuries that were reported in female ice hockey (96
per cent of the total) were categorised as contact injuries (Schick and
Meeuwisse 2003). NCAA data mirrored this finding with approximately half
of all injuries sustained during women’s collegiate ice hockey involving player
contact (Agel et al. 2007a). Even so, data from Canadian collegiate
competition indicated the severity of injuries suffered in collegiate women’s
ice hockey was less in terms of time lost subsequent to injury – the male
collegiate players in the study reportedly sustained a much higher number of
injuries which were categorised as severe (resulted in more than fourteen
missed sessions following injury) (Schick and Meeuwisse 2003).
As is the case with male players, the most common injury in women’s
collegiate ice hockey in Canada was reported to be concussion; the next most
common injuries were ankle sprains and adductor muscle strains (Schick and
Meeuwisse 2003). NCAA data were broadly similar – concussions being the
most common injury (21.6 per cent of total injuries), with knee internal
derangement (12.9 per cent of total) and shoulder – specifically
acromioclavicular joint injury – (6.8 per cent of total) being next common
(Agel et al. 2007b). Canadian male collegiate players also suffered a number of
facial injuries, which were not reported at all during collegiate women’s ice
hockey participation in Canada (Schick and Meeuwisse 2003).
Analysis of risk factors for injury prevention training
interventions
In addition to players’ routine strength training, particular strength and
neuromuscular training exercises may also be prescribed to specifically guard
against common injuries reported in the sport. This specific injury prevention
role for strength training has not received the research attention it would
appear to merit. Too often, specific strength exercises are only prescribed for
team sports players once an injury has already occurred (Wagner 2003).
Although there are a growing number of studies detailing injury data for
different sports, there are very few that assess injury prevention strategies for
sports. For example, despite soccer’s status as the most popular sport in the
world, a review of the literature pertaining to injury prevention for soccer
players found only four relevant studies that met inclusion criteria (Olsen et
al. 2004).
The process of specific training prescription should begin with a needs
analysis of the particular sport, including research into the injuries commonly
sustained during competition. After examining injury data for the sport, the
injury history of each player and any ongoing injury concerns will then help
to highlight the specific needs of each individual. Such analysis of the sport
combined with an assessment of the individual will identify what areas of the
body are prone to what type of injury.
Once identified, the design of the injury prevention intervention
programme should aim to systematically address risk factors for each specific
injury identified for the sport and the athlete (Nicholas and Tyler 2002). Such
preventative measures can only be taken by first gaining an understanding of
the causative factors and injury mechanisms that are characteristic of the
particular injury (Bahr and Krosshaug 2005). Such data for injuries that are
representative of different team sports are increasingly available (Junge and
Dvorak 2004) – and these are summarised in the next section.
Risk factors and injury mechanisms for identified
injuries
Ankle complex
The lower leg is the most frequent site of injury in the majority of sports
(Thacker et al. 2003). Ankle sprains comprise up to a third of all injuries
sustained during participation in sports (Osborne and Rizzo 2003). Once
injured, the risk of subsequent re-injury to the ankle is greatly increased
(Osborne and Rizzo 2003). Elite and recreational basketball players with a
history of ankle injury were reported to have a five times greater likelihood of
sustaining an ankle injury (McKay et al. 2001). Collegiate American football
players who had suffered previous ankle injury are similarly reported to suffer
six times higher ankle injury incidence (Tyler et al. 2006).
Ankle inversion sprain injury
Ligament laxity is commonly observed following ankle sprain injuries, which
results in decreased mechanical stability provided to the ankle joint
(Wikstrom et al. 2007). In addition to this reduced mechanical stability postinjury, neuromuscular and proprioceptive function is frequently also
impaired; the function of afferent sensors originating in the joint are often
disrupted following ankle ligament injury (Lephart et al. 1998). A consequence
of this interference in somatosensory feedback is that the player is less able to
sense joint position and motion at the ankle joint (Hertel 2008). This
disruption of proprioception and neural control post-injury is termed
‘functional ankle instability’, and is associated with deficits in postural
balance and ‘dynamic stabilisation’ (see Chapter 3) (Wikstrom et al. 2007).
In severe cases, recurrent ankle injury can lead to chronic ankle instability
(CAI), which describes a pattern of recurrent ankle sprain injury with
persisting symptoms of instability, such as episodes of the ankle giving way
during normal activities. Various sensorimotor and mechanical deficits have
been identified in those suffering with chronic ankle instability (Holmes and
Delahunt 2009). This typically includes a combination of both mechanical
instability, resulting from physical changes to joint and connective tissue
structures from the initial injury or injuries, and functional instability due to
reduced proprioception and kinaesthetic sense and a diminished ability to
sense and regulate force output (Hertel 2008).
Mechanical and functional instability of the ankle following injury is
demonstrated by the observation that corrective taping or external bracing to
provide added stability are effective in reducing subsequent injury incidence
(McKeon and Mattacola 2008). External support in the form of strapping or
ankle braces is, however, only effective in reducing injury in athletes who
have previously sustained ankle sprains (Osborne and Rizzo 2003;
Stasinopoulos 2004). Furthermore, the protective effect of external support
offered by bracing appears to diminish with recurrent exposure to ankle
sprain injury. Volleyball players with four or more previous ankle sprains
appear to experience no benefit from external ankle bracing (Stasinopoulos
2004).
The first-time incidence of ankle injuries (for players without any history of
lower limb joint injury) appears to be influenced by gender, with a trend for
more ankle inversion sprains suffered by female high school and collegiate
players (Beynnon et al. 2005). The female basketball players studied were
reported to suffer a significantly greater number of first-time ankle inversion
injuries than male basketball players. Among female players, the type of field
team sport they participate in also appears to influence first-time incidence of
ankle sprain injury: female basketball players report more first-time ankle
sprains than female lacrosse players (Beynnon et al. 2005). This does not
appear to be the case for male high school and collegiate players.
A large proportion of ankle inversion sprains in team sports occur when
landing with a plantar-flexed ankle position in combination with forced
inversion upon touchdown. Often the mechanism for ankle injuries sustained
during landing involves contact with another player (Kofotolis and Kellis
2007). For example, in volleyball ankle injuries often occur as a result of
landing on the foot of a team-mate or opponent in the area proximal to the
net (Verhagen et al. 2004). In the same way, landing – often onto the foot of
another player – was reported to account for almost half the ankle injuries
sustained by elite and recreational basketball players (McKay et al. 2001).
A common injury mechanism for non-contact ankle injuries is twisting or
turning the ankle when changing direction (McKay et al. 2001). As a
consequence of the associated impairment of mechanical and functional
stability players with previous ankle injury are more vulnerable to these
injuries. The combination of high body mass index and a history of previous
ankle injury appears to render players at further heightened risk of noncontact ankle injury. Collegiate American football players with both high
body mass index and history of ankle injury are reported to be at nineteen
times greater risk compared to players with normal body mass index and no
previous ankle injury (Tyler et al. 2006). The greater inertia of heavier players
challenges their ability to control their own momentum during change of
direction movements to a greater extent and increases forces exerted on the
supporting foot and ankle. The interaction of these greater forces with the
lingering mechanical and functional instability of the previously injured ankle
can then place the player’s capacity to dynamically stabilise the ankle closer
to its failure limits (Tyler et al. 2006).
Syndesmotic high ankle sprain injury
Although less common than lateral ankle sprain, syndesmotic or high ankle
sprains comprise a considerable number of ankle injuries sustained in contact
sports (Williams et al. 2007) – notably high incidence is reported in ice hockey
(Flik et al. 2005). This injury involves the ligaments associated with the distal
tibia and fibula. The classic injury mechanism for syndesmotic ankle sprain
involves application of an external rotation force while the ankle is
dorsiflexed and the foot is pronated – the key factor being that the talus is
forcefully rotated with respect to the lower leg (Williams et al. 2007).
Syndesmotic ankle sprains typically result in more time lost subsequent to
injury in comparison to lateral inversion sprains. Particularly severe
disruption of the ligaments (categorised as grade III syndesmotic injury) can
require surgical intervention. Lack of awareness has been identified as a factor
in syndesmotic ankle sprain injuries being underdiagnosed until recently.
Similarly, there is currently a lack of data regarding these injuries –
particularly with respect to rehabilitation and prevention of syndesmotic
ankle sprain injuries (Williams et al. 2007).
Knee
Knee ligament injury
Knee injuries are among the most debilitating injuries to which team sports
players are exposed (Thacker et al. 2003). Of all injuries, knee injury –
particularly to the ACL and MCL – is associated with the longest enforced
absences from practice and competition (Thacker et al. 2003). In two-thirds of
cases complete ACL rupture is accompanied by damage to knee cartilage,
causing further impairment of function and mechanical instability (Silvers and
Mandelbaum 2007). At their most severe, injuries to the knee can even be
career ending – particularly in the case of ACL injury. Following
reconstructive surgery to repair complete ACL rupture long-term pathology is
also often seen, including premature onset of osteoarthritis in later life (Silvers
and Mandelbaum 2007). Unlike ankle injuries for which external bracing has
been shown to help reduce risk of repeat injury, prophylactic bracing for the
knee has not been demonstrated to have any positive impact upon injury rates
(Hewett et al. 2006b; Silvers and Mandelbaum 2007). This underlines the
importance of training interventions to address knee ligament injury risk
(Hewett et al. 2005).
A history of previous knee ligament injury is a major risk factor for
suffering subsequent injuries. Following injury, the knee often exhibits
mechanical instability due to physical changes, such as increases in joint
laxity, as well as functional instability due to disrupted somatosensory and
proprioceptive function (Ingersoll et al. 2008). These factors lead to a
significantly increased risk of re-injury (Murphy et al. 2003). Those who are
ACL-deficient or have a reconstructed ACL following surgical intervention
exhibit impairments in somatosensory function, some of which persist for an
indefinite period (Ingersoll et al. 2008). The disruption of proprioceptive
function also appears to endure longer at smaller angles (15 degrees) of knee
flexion (Lephart et al. 1998). Neural inhibition affecting the quadriceps and
hamstring muscles in particular is also observed post-ACL injury, which
affects both strength and function (Ingersoll et al. 2008). The twelve-month
period following surgical ACL reconstruction has been identified as a critical
phase during which players are susceptible to repeat injuries to the same knee
(Orchard et al. 2001). Beyond this period, players continue to be more prone to
suffering another ACL injury; and this risk concerns both the uninjured and
previously reconstructed knee equally.
Team sports players are particularly liable to suffer injuries to the knee;
these can occur with or without direct contact. In particular, ACL rupture
commonly results from a non-contact injury mechanism (Chappell et al. 2002)
– more than two-thirds of ACL injuries occur in the absence of direct physical
contact from other players (Hewett et al. 1999, 2006a). Non-contact knee
injuries commonly occur when deceleration is combined with change of
direction with the foot planted (Silvers and Mandelbaum 2007). This risk is
greater when landing or changing direction with the lower limb in a relatively
extended position (Ford et al. 2003; Hewett et al. 2006b, Quatman et al. 2006).
The elements of jumping, landing and changing direction that feature in team
sports therefore expose players to knee injury risk.
Collision sports such as football and rugby football have the added risk of
contact knee injury. Players in these sports must perform multidirectional
movements under resistance from opponents and also sustain direct impact
during tackles, and this is reflected in greater incidence of contact ACL
injuries and MCL injuries in particular (Thacker et al. 2003). This is illustrated
by NCAA injury data reporting greater incidence of ACL injury in male
collegiate lacrosse in comparison to soccer and basketball, which was
attributed to the differing levels of direct physical contact permitted in these
sports (Mihata et al. 2006).
Sidestep cutting movements are identified as increasing knee valgus and
internal tibia moments of force and anterior loading on the knee (Kaila 2007),
all of which place the ACL under strain. During sidestep cutting movements
specifically, it is this valgus loading rather than anterior shear forces in a
sagittal plane that is the more likely cause of ACL rupture, in view of the
relative magnitude of strain involved (Silvers and Mandelbaum 2007). These
torsional forces and potential risk of ACL rupture are greater if the sidestep
cutting manoeuvre is executed with the tibia internally rotated and/or the
planted foot is in a pronated position (Silvers and Mandelbaum 2007).
Joint kinematics and associated loads are shown to differ considerably
between unanticipated versus pre-planned sidestep cutting movements.
Specifically, although knee flexion and/or extension moments do not appear
to be markedly different, valgus and internal rotation moments of force at the
knee joint were significantly greater during sidestep cutting movements
initiated in reaction to an external cue (versus pre-planned) (Besier et al.
2001). The fact that players are unable to pre-plan postural adjustments under
unanticipated conditions therefore results in altered lower limb kinematics
and joint loads, which in turn pose greater potential risk of injury to both
ACL and MCL (Besier et al. 2001). Team sports players are thus exposed to
particular knee injury risk – for example, when performing evasive sidestep
cutting manoeuvres to avoid opposing players (McLean et al. 2004).
It is widely documented that female players suffer significantly higher ACL
injury incidence – between two and ten times greater reported incidence
depending on the sport (Silvers and Mandelbaum 2007). Various anatomical
and biomechanical factors have been suggested to contribute to the higher
knee injury rates demonstrated by adolescent and adult female team sports
players (Ford et al. 2003; Noyes et al. 2005). A cadaveric study of mechanical
properties of the human knee report that at low knee flexion angles the female
knee possesses significantly less passive joint stiffness (25 per cent) under
torsional loads and also greater joint laxity in rotation (28 per cent) compared
to those of males (Hsu et al. 2006). This apparently inherent reduced
mechanical stability of the knee joint in female players is often also
compounded by adverse lower limb biomechanics.
Part of the disparity between genders may in part originate in growth and
maturation effects, on the basis that such differences in ACL injury rates are
not apparent prior to puberty (Hewett et al. 2006b). Increases in lever length of
the lower limbs during puberty are compounded by increases in body mass,
which are not accompanied by any natural gains in strength in female
athletes. As a result, the female player faces greater challenges controlling
motion of the trunk and exerting proximal control of the lower limb following
puberty. Female athletes therefore often exhibit ‘ligament dominance’ – that
is, in the absence of active muscular stabilisation they are over-reliant on
ligaments to support the lower limb joints (Ford et al. 2003). As a consequence
of these changes, female athletes also exhibit characteristic postural control
traits and lower limb biomechanics during standard athletic tasks, which place
them at greater risk of knee ligament injury (Barber-Westin et al. 2006;
Quatman et al. 2006).
For example, female players are reported to have a marked tendency
compared with males to execute athletic movements in an upright posture
with the lower limb relatively extended and the upper leg in an inwardly
rotated position (Leetun et al. 2004). This places the knee joint in a less
mechanically stable position; this is reported to occur frequently in female
athletes, particularly when landing or changing direction (Thacker et al. 2003).
When studied during pre-planned sidestep cutting movements it was similarly
noted that female subjects showed markedly different hip, knee and ankle
and/or foot joint angles and more variable knee rotation motion, compared
with males (McLean et al. 2004).
These postural traits during landing and sidestep cutting mean more force
must be absorbed through the knee and ankle joints, and it is evident that
female athletes also typically fail to fully recruit the hip musculature to assist
and help control lower limb motion (Hewett et al. 2006b; Landry et al. 2007).
The role of lumbopelvic control and hip muscle function in providing
proximal neuromuscular control to the lower limb has been highlighted
(Mendiguchia et al. 2011); this has been directly implicated in the mechanisms
for ACL injury (Hewett and Myer 2011).
The role of the lumbo-pelvic-hip complex with respect to ACL injury also
includes the capacity to control the position and motion of the trunk during
athletic movements (Myer et al. 2008). A prospective study identified that a
measure of lateral trunk strength was a significant predictor of female but not
male athletes who suffered knee ligament injury and ACL injury in the study
period (Zazulak et al. 2007). The capacity to control lateral lean of the trunk
was strongly associated with ACL injury incidence in the female athletes
studied (Zazulak et al. 2007). This is supported by a recent investigation of
video captures of ACL injuries: analysis of video footage identified that lateral
trunk lean in combination with increased abduction angle at the knee joint
was present in the female athletes as they sustained ACL injury (Hewett et al.
2009). This pattern was not found in equivalent video captures of male
athletes suffering ACL injury.
Neuromuscular recruitment patterns also appear to differ in females
(Hewett et al. 2006b). For example, female players have a greater tendency for
preferential recruitment of quadriceps over hamstrings; this phenomenon is
known as ‘quadriceps dominance’ (Ford et al. 2003). The action of the
quadriceps can increase anterior shear at the knee joint, and in turn increase
the strain on the ACL (Silvers and Mandelbaum 2007). In contrast, the
hamstrings compress the knee joint and oppose anterior shear forces during
weight-bearing closed-chain movements; as a result of these functions the
hamstrings muscle group is described as an ‘ACL-agonist’ (Hewett et al. 1999).
This quadriceps-dominant muscle recruitment strategy is therefore potentially
injurious to the ACL in female players.
Similarly, differences in gastrocnemius recruitment during unanticipated
sidestep cutting have also been reported between female and male adolescent
soccer players (Landry et al. 2007). Activation of the gastrocnemius,
particularly in combination with quadriceps activation, has the potential to
increase strain on the ACL. Female players displayed both higher overall
activation of the gastrocnemius and an apparent imbalance in recruitment
between medial and lateral gastrocnemius, with relatively greater activation
of lateral gastrocnemius (Landry et al. 2007).
Patellar tendinopathy
Aside from injuries to the knee ligaments and joint cartilage, chronic overuse
injuries associated with the patellar tendon are also common in jumping
sports particularly. Incidence of patellar tendinitis or ‘jumper’s knee’ is
notably high among volleyball players (Gisslen et al. 2005). Although
debilitating, players will often continue to train and compete while suffering
symptoms of this overuse injury (Verhagen et al. 2004). Particularly serious
cases can be career threatening, and surgical intervention may be required
(Kettunen et al. 2002).
Understanding of the underlying pathology of patellar tendinopathy is
incomplete – from relevant studies it appears to not be an inflammatory
condition. Patellar tendinopathy appears to be multifactorial – a range of
musculoskeletal factors may be present, and the specific combination appears
to vary between individual cases. The consensus is that suboptimal tracking of
the patella and associated stresses on connective tissues play a role in the
mechanism for this injury (Cowan et al. 2009). Accordingly, patellar
tendinopathy is commonly associated with sports that involve high knee
extensor torques and repeated jumping movements (Visnes and Barr 2007).
Risk factors for patellar tendonitis include reduced flexibility of the
hamstring and quadriceps muscles, which is postulated to increase strain on
the tendons (Witvrouw et al. 2001). Muscular imbalances or reduced eccentric
strength are also identified as potential risk factors. Imbalances in function of
muscles and/or connective tissue structures medial and lateral to the knee
joint have the potential to disrupt the tracking of the patella. Symptomatic
subjects are often identified as having altered activation and possibly atrophy
of the VMO versus vastus lateralis muscle; however, this is not always the
case (Cowan et al. 2009). The function of hip muscles that contribute to
lumbopelvic stability and proximal control of the lower limb are also
identified as possible factors in the development of patellar tendinopathy
(Cowan et al. 2009). For example, isokinetic concentric and eccentric torques
in hip external rotation and eccentric hip abduction torques have been
reported to be impaired in subjects with patellofemoral pain (Boling et al.
2009). Deficits in lateral trunk flexion isometric strength have likewise been
reported in those suffering patellofemoral pain (Cowan et al. 2009).
Neuromuscular control issues relating to lower limb biomechanics are
similarly implicated with this injury (Cowan et al. 2009). In the presence of
some or all of these risk factors, players who perform high volumes of games
and practices involving repetitive execution of a particular movement
(classically jumping activities) tend to experience an insidious and progressive
onset of symptoms of patellar tendinitis.
Hamstrings
Hamstring injuries are commonly reported to be the most prevalent form of
noncontact injury in team sports such as soccer, rugby football, American
football and Australian rules football (Opar et al. 2012). An injury surveillance
study of the English professional soccer leagues identified hamstring injury to
be the single most frequent injury diagnosis (12 per cent of total injuries), with
particularly high incidence in the Premier League (28 per cent of total) mostly
occurring during running activities (Woods et al. 2004). Data from
professional rugby union in England support this observation: the majority of
hamstring injuries were sustained when running, although those sustained
while kicking are often the most severe (Brooks et al. 2006). Incidence of
hamstring injury within the sport is often higher among playing positions that
most frequently engage in high-speed running and change of direction
activities. For example, in rugby union a higher incidence of hamstring
injuries in matches (but not training) is reported for backs in comparison to
the forward positions (Brooks et al. 2006).
The majority of hamstring injuries (53 per cent) reported in English
professional soccer concerned the biceps femoris muscle (Woods et al. 2004),
which is a finding common to most sports (Opar et al. 2012). The typical site
of hamstring strain injury is close to the muscle–tendon junction (Peterson
and Holmich 2005). These injuries may be insidious in onset, resulting from
cumulative muscle damage, or the mechanism for injury may be a single
triggering event (Opar et al. 2012). Hamstring injuries are commonly
sustained when engaged in running activity (Woods et al. 2004; Brooks et al.
2006). The end of the swing phase and beginning of the stance phase are
identified as the points in the gait cycle where players are most prone to
hamstring injury when running (Opar et al. 2012). These phases feature high
eccentric loads while the hamstring muscle is stretched to its full length; and it
is also here that the transition between eccentric action to decelerate the leg
and concentric action to generate propulsion occurs (Woods et al. 2004). It has
also been suggested that the hamstring muscle is most vulnerable to strain
injury during this switch between eccentric and concentric action (Peterson
and Holmich 2005).
A number of modifiable risk factors have been identified with respect to
first-time hamstring injury. These include deficits in flexibility, lumbopelvic
posture, conditions of fatigue and imbalances in muscle strength and function
(Opar et al. 2012). Conditions involving high eccentric forces in combination
with strain loads, such as during kicking tasks, are also associated with
increased risk of hamstring strain injury (Opar et al. 2012). A greater
incidence of hamstring injuries has been reported for players entering the
game as substitutes versus starting players in English professional rugby
union (Brooks et al. 2006). Similarly, the occurrence of severe hamstring
injuries immediately was also reported to be greater following the half-time
break. These findings indicate that insufficient warm-up is an additional risk
factor for hamstring injury.
Pre-season hamstring flexibility scores of Belgian soccer players who went
on to sustain hamstring muscle injury during the season were found to be
significantly lower than those who did not suffer hamstring injury (Witvrouw
et al. 2003). This is not a consistent finding, however; the data regarding the
association between hamstring flexibility and risk of first-time hamstring
injury from other studies have been more equivocal (Opar et al. 2012).
Reduced hamstring flexibility has been identified in players following
hamstring injury (Croisier 2004) and this does appear to contribute to the
greater risk of recurrent hamstring injury (Opar et al. 2012). In addition,
reduced hip flexor flexibility was identified as a risk factor that was related to
the increased rate of hamstring injury reported for Australian rules football
players who were over the age of 25 (Gabbe et al. 2006).
Lumbopelvic posture, and specifically the presence of anterior pelvic tilt, is
also identified as placing the hamstrings under additional strain and thereby
at risk (Opar et al. 2012). In the absence of effective lumbopelvic stabilisation
from postural lumbopelvic and hip muscles, the hamstring muscles are
required to work to help stabilise the pelvis whilst simultaneously fulfilling
their locomotor function. Not only is this inefficient use of locomotor muscles
but it also accelerates the onset of fatigue: both of these factors can make the
hamstrings more susceptible to injury. Video analysis of hamstring injuries in
Australian rules football has also identified that a common injury mechanism
is running with the trunk in a forward flexed position (Verral et al. 2005). This
often occurs in the act of accelerating or reaching to pick up or catch a ball. A
lumbopelvic posture with the pelvis in an anteriorly tilted position can also
place the hamstrings in an elongated position, potentially imposing greater
strain on the hamstring muscles (Croisier et al. 2004).
The rising incidence of hamstring injuries towards the end of the playing
period is a scenario common to team sports including rugby football and
soccer (Brooks et al. 2006; Woods et al. 2004), which strongly suggests a
fatigue effect. The impact of residual fatigue is also evident in the observation
that the incidence of hamstring injury during a match is reportedly greater
when a higher volume of training was undertaken in the week preceding the
match (Brooks et al. 2006). A fatigued muscle can sustain less loading whilst
being stretched (Croisier et al. 2004). This effect of fatigue on the ability of the
muscle to absorb energy is complicated by the fact that the biceps femoris
hamstring muscle receives dual innervation – from this arises the theoretical
possibility of differential effects of fatigue within the same muscle (Croisier et
al. 2004). Parts of the muscle innervated from one source might be at a more
advanced state of fatigue, hence operating with different contractile properties
to other parts of the muscle. The high incidence of hamstring injury in team
sports is believed to be in part due to the requirement to perform repeated
bouts of high-intensity work during the course of extended playing periods
(Verral et al. 2005).
The association between imbalances in strength and function with
hamstring strain injury has been investigated in soccer players at elite level.
Bilateral asymmetry (that is, difference between dominant and non-dominant
lower limb) between concentric and eccentric strength of both hamstrings and
quadriceps, the ratio between quadriceps versus hamstrings concentric
strength scores and a ‘mixed ratio’ of concentric quadriceps versus eccentric
hamstrings strength have all been used to evaluate strength imbalances. A
study of professional soccer players identified that imbalances in two or more
of the isokinetic test measures listed above when measured during pre-season
was related to incidence of hamstring strain injury during the subsequent
playing season (Croisier et al. 2008).
History of previous injury is a major risk factor for hamstring injury (Verral
et al. 2005). A large proportion of the hamstring strains reported in team
sports such as soccer are recurrent injuries (Arnason et al. 2008). There is
accordingly a high rate of re-injury reported with hamstring strain injuries in
team sports. Re-injury rates reported in the literature range from 14 to 63 per
cent, depending on the sport, the severity of the initial hamstring injury, and
the length of the follow-up period (up to two years) (Peterson and Holmich
2005; de Visser et al. 2012). Furthermore, repeat injuries sustained are often
more severe than the initial injury (Brooks et al. 2006). The first month
following return to play appears a critical period: it was during this time
interval that over half (59 per cent) of the total re-injuries were reported to
occur in data from English professional rugby union (Brooks et al. 2006). The
failure of standard rehabilitation programmes employed in sport to reduce the
rates of re-injury over the past three decades, despite extensive research
attention during this period, has recently been highlighted in the literature
(Mendiguchia et al. 2012).
Following injury, a variety of structural and functional changes may be
observed (Opar et al. 2012). For example, scar tissue formation may be
observed in scans of the hamstrings muscle up to one year following return to
competition post-injury (Mendiguchia et al. 2012). Alterations in muscle
activation are also evident following hamstring strain injury (Sole et al. 2012).
Such changes are often accompanied by changes in the length–tension
relationship of the previously injured muscle. The increased risk of re-injury,
even after extensive rehabilitation has been followed and full function appears
to have returned, are attributed to these persisting effects on the hamstrings
muscle length–tension relationship (Opar et al. 2012).
There is some suggestion that a proportion of posterior thigh injuries
presenting clinically as hamstring strains are in fact of lumbar spine origin –
as indicated by a negative MRI scan for hamstring muscle strain injury
(Orchard et al. 2004). It is believed this is a consequence of the L5–S1 nerve
supply of the hamstring muscles (for the same reason, athletes may also
present with calf muscle pain). Impingement or entrapment of the nerve root
in the lumbar spine region may cause symptoms characteristic of muscle
injury (Orchard et al. 2004).
The groin triangle
Adductor or ‘groin strain’ injury is commonly reported in many team sports –
in particular ice hockey, soccer and Australian Rules football (Maffey and
Emery 2007; Nicholas and Tyler 2002). A further complication with players
presenting with groin pain is that medical staff, trainers and coaches must also
be vigilant for more serious conditions such as osteitis pubis and sports hernia
(Lynch and Renstrom 1999). Likewise, potentially serious medical conditions
that can produce similar symptoms must also first be ruled out.
Injuries to the groin that are typically reported in team sports can be
divided into acute injuries with a sudden onset and overuse injuries. Acute
injuries are usually associated with greater time loss, in terms of forcing
players to miss practices and matches, whereas in the case of overuse injury
players often elect to continue to train and play despite persisting symptoms
of groin pain (Engebretsen et al. 2010). A common injury mechanism for acute
adductor muscle injury identified with field sports players is sudden forceful
external rotation of the hip whilst the upper leg is in an abducted position
with the foot planted (O’Connor 2004). The high incidence of adductor muscle
injury is attributed to the elements of multidirectional acceleration and
change of direction at high speed that are common to many team sports. The
adductor muscles’ role in stabilising and decelerating the lower limb also
involves a high degree of eccentric loading, and this has similarly been
implicated in the high incidence of strain injury (Tyler et al. 2001).
Previous injury is consistently reported as a risk factor for groin injury
(Engebretsen et al. 2010). For example, a study of professional ice hockey
players reported that a history of previous injury within the preceding year
was a significant risk factor for suffering further adductor muscle strain injury
(Emery and Meeuwisse 2001). Groin injury is also associated with a high rate
of recurrence (Arnason et al. 2004; Maffey and Emery 2007; Nicholas and
Tyler 2002), and traditional passive rehabilitation methods appear relatively
ineffectual for treating groin pain. It has therefore been identified that in order
to be effective, interventions should feature active strengthening exercises to
restore strength and function of the adductor muscles (Tyler et al. 2002).
Adductor muscle weakness measured by clinical isometric strength
assessment during pre-season was identified as a risk factor that was
associated with the incidence of new groin injuries suffered by male soccer
players during the subsequent playing season (Engebretsen et al. 2010).
Imbalance between adductor and abductor muscle strength measures is also
identified as a major risk factor for adductor muscle strain injury (Nicholas
and Tyler 2002). A study of a professional ice hockey team reported that if a
player’s pre-season adductor strength test scores were less than 80 per cent of
their strength scores for abduction they had a significantly higher incidence of
adductor muscle strain during the subsequent season (Tyler et al. 2001).
Similarly, players who start the season in a deconditioned state appear
more prone to suffering adductor strain injury (Maffey and Emery 2007).
Players who had failed to complete a certain number of off-season training
sessions suffered a higher incidence of adductor muscle injuries when they
reported to pre-season training camp (Emery and Meeuwisse 2001). This
strongly suggests that fatigue is a risk factor for adductor strain injury, in
much the same way as it is for hamstring strains.
Similar to the findings concerning hamstring injury risk, a relationship has
been identified between impaired adductor muscle flexibility and risk of
adductor muscle strain. Baseline scores of passive hip range of motion in
abduction were found to be associated with subsequent incidence of adductor
muscle injury in soccer players (Arnason et al. 2004). This association was not
found in a study of professional ice hockey players, suggesting the influence
of adductor muscle flexibility on injury risk may depend upon the sport (Tyler
et al. 2001).
Deficits in lumbopelvic stability have also been identified as a risk factor for
adductor strain injury (Maffey and Emery 2007). Impaired function of deep
lumbar stabiliser muscles has been implicated in players with a long-term
history of groin pain. Deficiencies in the way in which force is transmitted
from the locomotor muscles to the torso, as a result of suboptimal function of
muscles that stabilise the pelvis and lower limb, may expose the adductor
muscles to injury risk (Maffey and Emery 2007). In the presence of instability
at the pelvis or lower limb malalignment, the adductor muscles may try to
compensate, thus placing them under additional strain (Lynch and Renstrom
1999). It has therefore been suggested that treatment for groin pain should
include active strengthening for the hip and abdominal muscles that help
provide lumbopelvic stability.
Lumbar spine
After the ankle and knee, the lower back is commonly reported to be the third
most common site of injury in sports (Nadler et al. 2000). This is particularly
the case in sports involving striking or throwing movements which require
rotation of the hips, pelvis and spine (Harris-Hayes et al. 2009). Female
athletes in particular also appear prone to low back pain and injury. A study
of injury incidence among NCAA collegiate athletes for the 1997/98 season
indicated almost twice the number of lower back injuries in females (Nadler et
al. 2002).
The mechanism for low back pain and injury is often cumulative; there
may or may not be a single triggering event (McGill 2007b). Similarly, a
distinction must be made between acute back pain or injury and chronic
conditions. Acute episodes of low back pain respond well to rest and
treatment or even resolve spontaneously (Rogers 2006). Conversely, chronic
lower back problems (lasting longer than three months) do not respond to rest
or passive therapies; in these cases the consensus is that active approaches
involving appropriate training interventions are most effective (Danneels et al.
2001).
The observation that when stripped of supporting musculature a cadaver
human spine will buckle under 20lb (≈9kg) of load illustrates the contribution
made by the various supporting muscles in providing active spine stability
(Barr et al. 2005). Low back pain is often accompanied by disrupted motor
patterns of various stabilising muscles (Rogers 2006). A common finding is
that deep lumbar spine stabiliser muscles are atrophied in individuals with
chronic lower back pain (Barr et al. 2005). Importantly this atrophy does
appear to be reversible with appropriate training intervention, with associated
improvements in low back pain symptoms (Hides et al. 2001). Individuals with
chronic lower back pain also exhibit impaired neuromuscular feedback and
delayed muscle reaction, which is accompanied by reduced capacity to sense
the orientation of their spine and pelvis (Barr et al. 2005). There is some
debate whether these functional deficits are primarily a cause or consequence
of chronic low back pain (McGill 2007b).
Team sports require both strength and endurance for the muscles that
stabilise the spine in all three planes of motion (Barr et al. 2005; Leetun et al.
2004). Weakness or impairment at any point in this integrated system of
support can lead to damage to structural tissues (ligament and articular
structures), causing injury and pain (Barr et al. 2005). Imbalances in strength
and endurance of flexors and extensors of the trunk have also been implicated
as a risk factor for low back pain (Rogers 2006). Endurance rather than
absolute strength of trunk muscles has been identified as being the most
decisive factor with regard to low back pain incidence (McGill 2007b).
The hip musculature serves a major role in stabilising the pelvis during all
dynamic activities performed in an upright stance or weight-bearing through
the lower limbs (Nadler et al. 2000). Impaired function of the hip extensors
and hip abductors are observed with athletes who are suffering lower back
pain (Nadler et al. 2002). Strength imbalances in these muscles are also
implicated in lower back pain incidence, particularly in female athletes
(Nadler et al. 2000). Isometric hip external rotation strength was identified as
the single best predictor of lower back and lower extremity injury incidence
in collegiate athletes (Leetun et al. 2004). Inflexible or weak hip rotators can
also predispose the athlete to poor pelvic alignment; excessive lumbar spine
motion can also occur in an attempt to compensate for impaired hip rotator
function (Regan 2000). Both of these factors can lead to pain and the incidence
of lumbar spine injury.
Shoulder complex
As a consequence of the high degree of mobility of the shoulder joint, it is
heavily reliant on dynamic (that is, muscular) stability (Wagner 2003). Active
stabilisation is provided by the co-ordinated function of a number of muscles,
in particular those that control the articulation between the scapula and
thorax, and the ‘rotator cuff’ of muscles at the glenohumeral joint (Myers and
Oyama 2008). The co-ordination and synergistic function of the various
stabilising muscles is controlled via an integrated sensorimotor system that
relies upon afferent input from mechanoreceptors within the muscles and
connective tissues structures. Any disruption to these structures or alteration
in function of the individual muscles that contribute to providing dynamic
stabilisation will therefore have major consequences for the structural
integrity of the shoulder complex and the corresponding risk of injury.
Acute shoulder injury
In collision sports, such as rugby football, American football and ice hockey,
injuries to the shoulder represent a leading cause of lost participation in
training and matches. In a study of professional rugby union in England the
number of days lost to shoulder injuries was reportedly second only to knee
injuries (Headey et al. 2007). Similarly high incidence of shoulder injury is
reported in American football: half of all elite collegiate players participating
in the 2004 NFL Combine reported history of shoulder injury; and of these
players a third had previously undergone shoulder surgery (Kaplan et al.
2005). A study of ice hockey injuries in Finland likewise identified a high
number of shoulder injuries among players of various ages, particularly those
in the 20–24 and 25–29 age groups. The majority of the reported injuries (79
per cent) were the result of body checking or other collisions with players or
the boards surrounding the ice rink (Molsa et al. 2003).
Contact shoulder injuries in collision sports most often occur during
tackles. Accordingly, playing positions with the greatest exposure to tackle
situations generally, and high-speed collisions in particular, typically report
the highest incidence of shoulder injuries (Headey et al. 2007).
Acromioclavicular (A-C) joint separations are the most commonly reported
type of injury among elite collegiate American football players (Kaplan et al.
2005). Anterior instability is another common condition that was reported –
predominantly affecting defensive positions among this sample of elite
collegiate players (Kaplan et al. 2005). A study of English professional rugby
also reported that the most common contact injuries sustained by players
were A-C joint injuries (Headey et al. 2007). The most severe tackle injury
involving the shoulder in English professional rugby union, in terms of time
lost subsequent to injury, was shoulder dislocation (Headey et al. 2007).
Rotator cuff tears and impingement injuries are also frequently reported
among both English professional rugby players (Headey et al. 2007) and elite
collegiate American football players (Kaplan et al. 2005). Rotator cuff tears
appear to be most commonly sustained from direct impact on the shoulder as
a result of a fall or collision with another player.
The incidence of shoulder injury in English professional rugby union
football is reported to be highest in the final quarter of matches and during
the latter stages of training sessions (Headey et al. 2007). This finding implies
a fatigue element in the incidence of contact shoulder injuries in collision
sports. It has also been proposed that repeated exposure to impact forces
during collisions may lead to cumulative microtrauma, which in turn could
potentially lead to impaired active and passive stability of the shoulder
complex. Biochemical markers of muscle damage following a competitive
rugby match showed that the degree of muscle damage was directly linked to
the number of tackles each player had performed and sustained during the
course of the match (Takarada 2003). Such muscle damage results in shortterm reductions in function, which are fully restored after a period (several
days) of recovery. The training status of the player also has a major effect on
the degree of muscle damage following strenuous physical exertion (Takarada
2003).
There is a high rate of re-injury reported with shoulder injuries – 27 per
cent of all shoulder injuries reported in a study of professional rugby union in
England were recurrences of previous injuries (Headey et al. 2007). Following
acute injury trauma and disruption to connective tissues and joint structures
may be observed, which may result in reduced mechanical stability. Even in
the absence of changes in mechanical stability there are typically changes in
functional stability following injury due to persisting effects on sensorimotor
function from the initial trauma (Myers and Oyama 2008). Sensorimotor
deficits and alterations in function of the muscles that provide stability to the
glenohumeral joint and control the articulation between scapula and thorax
have major consequences for the integrity and dynamic stabilisation of the
shoulder complex.
Recurrent injuries are also often more severe than new injuries in terms of
time lost subsequent to the injury (Headey et al. 2007). This is likely a
consequence of the persisting instability following injury leading to a reduced
ability to maintain joint integrity, and resist external forces during collisions,
once players have returned to training and competition. This high rate of reinjury appears particularly evident with dislocation and/or instability injuries;
these injuries were reported to have a 62 per cent recurrence rate among
English professional rugby union players (Headey et al. 2007). These findings
also reflect difficulties in achieving effective injury rehabilitation in order to
restore full function.
Overuse injuries of the shoulder complex
Overuse injuries of the shoulder complex can also be prevalent in team sports,
particularly those that involve throwing and striking, such as baseball and
volleyball. For example, imbalances and specific deficits in strength and
function of particular rotator cuff muscles are characteristically found in
overhead throwing and striking sports, which result in associated symptoms
of pain and impingement (Wilk et al. 2002). Repeatedly performing ballistic
throwing or striking movements during practice and competition can cause
progressive weakness of the muscles that work eccentrically to decelerate the
humerus and stabilise the glenohumeral joint, due to the cumulative stresses
and microtrauma involved (Behnke 2001). For example, specific atrophy of the
infraspinatus muscle accompanied by reduced external rotation strength
scores is evident in beach volleyball players (Lajtai et al. 2009).
Strength ratios of internal and external rotator muscles of the shoulder are
frequently employed to identify athletes at risk of overuse shoulder injury
(Niederbracht et al. 2008). In particular, reduced eccentric strength of external
rotator muscles relative to the concentric strength of internal rotators shows a
significant association with shoulder pain and injury in overhead sports
players (Wang and Cochrane 2001).
Aside from the development of imbalances or relative weaknesses,
repetitious sports activity and eccentric overload can also lead to impaired
sense of scapular position and control of scapula stabilisers (Wang and
Cochrane 2001). Such disruption in scapulohumeral rhythm (scapular
movement and positioning in response to movement of the upper arm) can
lead to glenohumeral joint instability (Brummitt and Meira 2006). This is
suggested to be a common mechanism leading to pain and injury particularly
in overhead athletes (for example, volleyball players) (Wang and Cochrane
2001).
Summary
Intrinsic risk factors have been described that can predispose a player to
sustaining injury. As discussed, playing a given sport exposes players to
conditions – ‘extrinsic risk factors’ – that may expose them to certain injuries.
Epidemiological data have been summarised that detail the incidence and
severity of injuries that are characteristic of participation in different team
sports. When a player who exhibits intrinsic risk factors is then exposed to
extrinsic risk factors by competing in a particular sport, all that remains is for
a triggering event to take place for an injury to result (Bahr and Krosshaug
2005). This triggering event pertains to the injury mechanism – typical injury
mechanisms have been summarised for the injuries commonly identified in
team sports.
Based upon this analysis, the next step is to design training interventions to
address those of the above risk factors that are reversible and attempt to
specifically guard against identified injury mechanisms. Such interventions
have the dual aim of reducing overall injury incidence and reducing the
severity of injuries sustained by players. Depending on the inciting event,
some injuries – such as those resulting from contact with an opponent – are
not avoidable; however, the severity of the damage that is sustained may be
limited by prior preventative training (Bahr and Krosshaug 2005).
10
TRAINING FOR INJURY PREVENTION
Specific training interventions
Introduction
Sport-specific physical conditioning can favourably influence a player’s injury
risk profile when training and competing in the sport. One general protective
effect is that appropriately conditioned players are more resistant to the
neuromuscular fatigue that renders athletes susceptible to injury (Hawkins et
al. 2001; Murphy et al. 2003; Verral et al. 2005). The importance of this is
illustrated in the common trend in many sports for higher injury rates in the
latter stages of matches when players are fatigued (Best et al. 2005; Brooks et
al. 2005a; Hawkins and Fuller 1999; Hawkins et al. 2001). Participating in a
pre-season conditioning programme was shown to reduce by more than half
the injuries sustained by female high school soccer players during the
subsequent season (Heidt et al. 2000). More sport-specific metabolic
conditioning appears more effective in guarding against these negative effects
of neuromuscular fatigue (Verral et al. 2005). In this way, the general
protective effect of metabolic conditioning regarding injury risk exhibits
specificity effects.
Strength training similarly serves a general protective effect in making the
musculoskeletal system stronger and thereby more resistant to the stresses
incurred during games (Kraemer and Fleck 2005). The addition of strength
training to the physical preparation of male collegiate soccer players was
followed by an almost 50 per cent reduction in injury rates during subsequent
playing seasons (Lehnhard et al. 1996). One aspect of this is that trained
muscle is more resistant to the microtrauma caused by strenuous physical
exertion and also recovers faster (Takarada 2003). The protective function of
strength training also exhibits specificity, as it is restricted to the bones and
connective tissues associated with the limbs and muscles employed during the
training movement.
However, conventional training alone is not sufficient to address critical
risk factors and neuromuscular control deficits identified for particular
injuries. For example, a strength-training intervention in isolation had no
significant impact upon the aberrant lower limb biomechanics that predispose
female players to knee injury, despite significantly increasing strength levels
(Herman et al. 2008). Targeted interventions have the potential to address such
risk factors in order to specifically guard against certain injuries to which
team sports players may be exposed.
Training for injury prevention comprises both safeguarding against firsttime injury and also reducing the risk of recurrence of previous injuries. The
previous chapter explored the risk factors relevant to the particular sport and
playing position, and the intrinsic risk factors that affect each individual
player. In this chapter we examine the specific neuromuscular and strengthtraining interventions that can be employed to address the risk factors and
injury mechanisms identified for the particular injuries that are commonly
seen in different team sports.
Approaching training for injury prevention
Often the injury prevention interventions that are employed both in studies
and in the field are essentially the same as those which have reported success
in a rehabilitation setting. This concerns not only the training mode and but
also other training parameters – such as frequency, intensity and volume
prescribed. For example, it is customary for many rehabilitation training
interventions to be performed with a daily frequency – eccentric training
regimens commonly prescribe training bouts to be performed twice daily
(Rees et al. 2009). Unfortunately, due to the relative shortage of studies
investigating injury prevention training interventions, a dose–response
relationship has yet to be established (Engebretsen et al. 2008). However, this
daily (or twice daily) frequency of training would seem contrary to what is
known about the time course for adaptation of muscle and connective tissues,
as well as what is known about the optimal range of training frequency to
elicit neuromuscular adaptations from the strength training literature. It has
been identified in the sports medicine literature that exercise prescription in a
rehabilitation and injury prevention setting typically does not account for
fundamental aspects of training design, such as variation, progression and
periodisation (Rees et al. 2009).
In terms of exercise selection, it is also yet to be resolved what the optimal
training modes might be for preventing specific injuries. While the training
interventions that have shown to be effective for the rehabilitation of specific
injuries would appear to be a sensible starting point, equally it should be
acknowledged that an uninjured athlete has very different requirements and
capabilities from an athlete who has recently sustained a particular injury. In
support of this contention is the observation that the ‘prophylactic’
application of standard rehabilitation protocols for particular injuries do not
appear to be particularly effective in reducing injury incidence for previously
healthy athletes (Engebretsen et al. 2008; Kraemer and Knobloch 2009).
The study by Fredberg and colleagues (2008), for example, employed lowintensity body-weight resistance exercises derived from rehabilitation
eccentric training protocols for Achilles and patellar tendinopathy. The
training intervention failed to reduce subsequent injury incidence in the
soccer players studied. In fact the injury rate of players who were
asymptomatic at the start of the study but showed abnormalities in their
Achilles and/or patellar tendon in their ultrasound scans prior to the
intervention was higher than the norm for the group in the subsequent season.
These results indicate the training intervention not only failed to serve any
preventative function but was also ineffective as an early treatment or
rehabilitation modality (Fredberg et al. 2008).
Based upon these observations, it appears that when approaching injury
prevention it is important to make a distinction between athletes who have a
history of injury versus those with no previous incidence. Those who are at
increased risk based on their injury history and/or ongoing deficits in function
can be easily identified via questionnaires or interviews and grading players’
responses using clinical assessment tools available in the sports medicine
literature (Engebretsen et al. 2010). As described in Chapter 2, there are
numerous clinical tests that can be employed for musculoskeletal assessment.
There are also a number of assessments of neuromuscular control and
function indicative of lower limb injury risk, detailed in Chapter 3. In the case
of athletes who report prior incidence of a particular injury it is important to
consider the specific risk factors identified for re-injury. From this viewpoint,
it is similarly important to consider the neuromuscular and sensorimotor
deficits that can result from particular injuries.
In this instance, the intervention employed to guard against (repeat)
incidence of injury might be broadly similar to the approach employed during
the latter stages of rehabilitation for that specific injury. However, it should be
noted that standard preventative interventions that feature rehabilitation
exercises are not shown to be effective in some studies, even among those
identified as being at high risk based on previous injury or reduced function
reported at baseline (Engebretsen et al. 2008). This suggests that the standard
‘rehabilitation’ approach to injury prevention training prescription may not be
sufficient even for previously injured athletes.
In any case, injury prevention for previously healthy athletes (with respect
to a particular injury) would appear to necessitate a less conservative and
more progressive approach, rather than merely employing the same training
prescription that is applied for rehabilitation. The threshold intensity or
neuromuscular challenge required to elicit the desired adaptation is likely to
be greater in a healthy versus an injured athlete. There will also be differences
in motivation between injured and uninjured athletes. Healthy athletes will
not have the same intrinsic motivation – undertaking the training
intervention in order to relieve pain and other symptoms – that an injured
athlete will. Likewise, in order to assist compliance in the longer term, as well
as facilitating continued adaptation, it is likely that there will be need for
reduced frequency and greater variation in terms of exercise prescription
when employing this form of training with healthy athletes to reduce training
monotony and boredom.
Integration of injury prevention training
Issues of adherence are frequently cited by investigations of injury prevention
interventions in the sports medicine literature (Emery and Meeuwisse 2010).
Poor compliance has been reported even among those identified as being at
particular risk of injury, in some cases resulting in a failure to complete even
the recommended minimum training frequency and volume required for a
prophylactic effect (Engebretsen et al. 2008). In general, adherence is much
better when injury prevention interventions are performed in a group setting,
compared to when exercises are prescribed to be performed in the athlete’s
own time. Similarly, one approach that shows a great deal of promise in terms
of resolving issues of compliance is to integrate the injury prevention
intervention into the players’ warm-up prior to training (Gilchrist et al. 2008).
It follows that injury prevention interventions should be performed in a
group setting, with appropriate supervision where possible. Furthermore,
compliance concerns not only adherence but also the quality of execution
(Engebretsen et al. 2008), which will also be determined by the player’s
attention and directed mental effort when performing the exercises set. From
this viewpoint, the greater the degree to which such interventions are
incorporated into players’ routine training, the better the level of compliance
is likely to be. For example, rather than performing interventions to develop
strength, muscle recruitment, and so on, as a stand-alone session, they should
be integrated into the player’s (supervised) strength training programme.
Likewise, corrective neuromuscular training prescribed might be incorporated
into speed and agility sessions, and dynamic balance and stabilisation
exercises performed as part of the players’ standard warm-up prior to
training.
Intensity and progression of training variables
As discussed in the previous section, it is likely that the intensity of
preventative or prophylactic training will need to exceed a threshold in order
to elicit adaptation in healthy tissues. Furthermore, in accordance with the
size principle, higher-intensity preventative training should aim to recruit the
higher threshold motor units that will come into play when the player is
operating at high velocity or against a high degree of external resistance, for
example during bodily contact with opponents.
Similarly, healthy athletes will tend to adapt more quickly and therefore in
order to avoid plateaus in the training response there will be a need for
progression. Equally the required rate of progression of different training
parameters will necessarily differ from what is typically seen in a
rehabilitation setting. By definition, an injured athlete has limitations that are
not present in an uninjured healthy athlete. It follows that the rate of
progression for athletes with a prior history of a particular injury will initially
be determined by set criteria, such as the return to baseline of specific
neuromuscular and sensorimotor capacities.
Injury prevention training interventions
Ankle
Developing proprioceptive function and the active stability provided by
muscles of the lower leg are key aspects of guarding against ankle injury for
athletes with or without previous history of ankle sprains. Afferent input from
mechanoreceptors within the muscles associated with the ankle joint serve the
dominant role in providing the athlete with a sense of joint position and
kinaesthetic awareness (Holmes and Delahunt 2009). Appropriate strength
training and neuromuscular training offer a means to develop the
proprioception provided by muscle mechanoreceptors. A variety of strength
training and neuromuscular training interventions have been shown to
improve measures of proprioception and ankle joint position sense specifically
(Holmes and Delahunt 2009).
Much of the increased risk of re-injury with ankle sprains is attributed to a
loss in proprioceptive function associated with the injured ankle. Taping the
lower limb and ankle joint is often employed particularly for players with
previous ankle sprain injury, in part as a means to augment proprioception
due to the cutaneous stimulation provided (Hopper et al. 1999). Those with a
history of ankle injury characteristically show deficits in sensorimotor control
leading to ‘functional instability’ (Hertel 2008), and this may be combined
with mechanical instability resulting from disruption to the ligaments and
joint capsule from the initial injury. The syndrome termed chronic ankle
instability (CAI) is a particularly severe example of this (Holmes and
Delahunt 2009).
Clearly, addressing and correcting these deficits must be a starting point for
interventions aimed at preventing re-injury. Those suffering with chronic
ankle instability exhibit reduced proprioception, and in particular an impaired
sense of ankle joint position in the frontal plane (Holmes and Delahunt 2009).
Similarly, kinaesthetic sense during movement may be impaired in those with
chronic ankle instability. Consequently, postural control and static balance are
often both reported to be reduced in those with chronic ankle instability, and
dynamic stabilisation is another aspect of neuromuscular control that is found
to be affected (Holmes and Delahunt 2009).
Training to develop proprioception in the previously injured ankle is
demonstrated to be effective in reducing the risk of re-injury (Osborne and
Rizzo 2003; Stasinopoulos 2004). A targeted single-leg balance training
intervention for high school football players deemed to be at high risk for
non-contact ankle injury was successful in reducing injury rates to the extent
that the injury risk factors of previous ankle injury history and high body
mass index were entirely offset in these players (McHugh et al. 2007). A study
of male soccer players with a history of previous ankle inversion injury
reported that of three preventive interventions studied (strength training for
evertor muscles, external bracing and proprioception training), only
proprioceptive ankle disc training successfully reduced the rate of re-injury
(Mohammadi et al. 2007). Training with a mini trampoline was reported to be
equally effective as balance disc training for reducing postural sway indicative
of functional ankle instability in recreational athletes with previous ankle
sprain injury (Kidgell et al. 2007). Importantly, the protective effect of
proprioceptive training appears to be maintained even with athletes with a
previous history of numerous (more than three) ankle sprains, which does not
appear to be the case with external bracing (Stasinopoulos 2004).
The training intervention most consistently found to be effective in the
literature for preventing first-time ankle sprains as well as recurrent injuries is
balance or proprioceptive training (McKeon and Mattacola 2008). For example,
a balance training intervention that was effective in reducing the incidence of
ankle sprain injuries in male and female high school soccer and basketball
players with a history of ankle sprains also reported a strong positive trend
(p=0.059) among players without prior ankle injury (McGuine and Keene
2006). The instances in the literature where equivocal results have been
reported for athletes without any history of ankle injury may simply reflect
that the proprioceptive training interventions employed in these studies was
insufficiently challenging.
Players who have not suffered prior ankle injury will not exhibit the
sensorimotor deficits associated with previous ankle injury, and given that the
baseline level of function is higher, it follows that more basic balance training
activities are unlikely to elicit significant improvements. For these players,
more challenging training modes to develop dynamic postural control and
dynamic stabilisation are likely to be more effective (Figure 10.2). The reader
is referred to Chapter 3 for definitions and descriptions of these training
modes.
The capacities required for maintaining equilibrium during normal gait and
landing activities comprise both feed-forward motor control and afferent
feedback from receptors in the joint, muscle and skin (Hertel 2008). Both of
these components are implicated in the sensorimotor deficits observed with
those suffering chronic ankle instability, and these abilities are therefore
affected in these players. Previously injured players should therefore also
progress to dynamic balance and dynamic stabilisation training modes, once
baseline levels of sensorimotor function have been restored. Indeed, this may
be a requirement for those with chronic ankle instability, in view of the
limited effectiveness often reported with standard static balance training
interventions in this subject population (McKeon and Hertel 2008). In support
of this contention, a progressive balance training programme, featuring a
variety of dynamic balance and dynamic stabilisation tasks under both preplanned and reactive conditions, was reported to elicit significant
improvements in function and measures of static and dynamic postural
control in subjects suffering with chronic ankle instability (McKeon et al.
2008). Higher training frequency appears to be beneficial with proprioceptive
or balance training interventions (McKeon and Mattacola 2008). It also
appears that additional benefits are conferred when the proprioceptive
training intervention is continued for a longer duration (McKeon and Hertel
2008b).
Deficits in strength of muscles that contribute to providing stability to the
ankle following injury have been identified as a factor in functional
instability. It is likely that transient reductions in strength are due in a large
part to neural inhibition, as strength deficits typically resolve during the
period following the initial injury (Hertel 2008). However, for players
suffering with chronic ankle instability, strength deficits may persist. In
contrast to clinical approaches that typically focus on the peroneal
musculature, based upon the literature it is the invertor muscles which
actually appear to be those most affected (Holmes and Delahunt 2009).
Appropriate strength training to restore function and develop strength for
these muscles is therefore recommended to help prevent re-injury. Closed
chain single-limb support exercises performed under external resistance in a
variety of planes are recommended for this purpose (Bellew and Dunn 2002).
In general, these exercises should be performed without shoes (to remove the
external support provided) and variations performed on labile surfaces such as
foam mats might also be considered.
In view of the fact that the majority of ankle injuries occur when landing or
changing direction, appropriate movement skills instruction and training is
also identified as a possible means of reducing ankle injuries (McKay et al.
2001). This may be particularly beneficial for players who have a history of
ankle sprains, in view of the fact that athletes have a tendency to exhibit
altered motor control strategies following injury (Wikstrom et al. 2007).
Retraining ‘correct’ movement mechanics would appear especially important
for players showing these signs of functional ankle instability. In support of
this, an intervention that consisted solely of instruction and practice of
jumping and landing technique was equally effective at reducing injuries
among female volleyball players as proprioceptive training and bracing
(Stasinopoulos 2004). Corrective neuromuscular training to develop postural
control and movement skills is discussed in detail in Chapter 3.
From the limited investigations into syndesmotic ankle injury that have
been published there are guidelines with respect to stages of treatment and
rehabilitation. There are currently no such guidelines for prevention strategies
for this specific injury. In the absence of this information, a good starting
point might be to follow the guidelines suggested for the final stage of
rehabilitation, which includes strength and neuromuscular training similar to
that employed to guard against lateral inversion sprain injuries.
Knee ligament injury
Interventions to reduce risk of knee ligament injury, and ACL injury
prevention for female players in particular, typically focus on addressing
documented biomechanical and neuromuscular risk factors via corrective
training (McLean et al. 2004). Studies with male athletes are currently
somewhat lacking but various neuromuscular training interventions have
been shown to reduce incidence of ACL injury with female team sports
players (Hewett et al. 1999; Mandelbaum et al. 2005). Effective interventions
that are documented to reduce rates of ACL injury generally comprise
multiple components, aimed at addressing a combination of neuromuscular
training outcomes. A range of training modes are employed, including
strength training, plyometrics, a variety of proprioceptive and balance training
modes, and movement skills training (Hewett et al. 2006a). One such example
is the Sportsmetrics protocol developed at the Cincinnati Sports Medicine
Research and Education Foundation (Hewett et al. 1999). Recently,
lumbopelvic training has also received increasing attention due to the
reported association between neuromuscular deficits in the capacity to control
trunk position and the mechanism of ACL injury with female athletes
(Zazulak et al. 2007)
Strength training, in combination with other forms of neuromuscular
training, is a common feature of most (but not all) successful knee injury
prevention protocols. Exercise selection should generally focus on developing
strength and recruitment of the proximal hip musculature (Myer et al. 2008)
and specific development of the hamstring muscle group would also seem to
be important. Reflex activation of the hamstrings originating from
mechanoreceptors at the knee joint is identified as crucial to dynamic
stabilisation of the knee joint (Lephart et al. 1998), reflecting the role of the
hamstrings as an ‘ACL agonist’ during weight-bearing closed-chain
movements (Hewett et al. 1999). The functional capacity of the hamstring
muscles is therefore an important factor contributing to dynamic stabilisation
of the knee. Hence, in addition to proprioceptive training, specific
strengthening of the hamstrings would also appear to be important for
developing the capacity to stabilise the knee during movement. This is
particularly relevant to female players for whom hamstring strength typically
plateaus early in their development: it is reported that hamstring strength
measures of older age groups (13–17 years) do not differ significantly from
those of 11-year-old females (Barber-Westin et al. 2006).
Effective training interventions for reducing risk and incidence of knee
injury generally feature some form of corrective movement skills training
(Silvers and Mandelbaum 2007). An apparently important feature of this
training is the inclusion of specific coaching with feedback regarding ‘safe’
versus ‘unsafe’ biomechanics (such as posture and lower limb alignment) for
athletic movements (Hewett et al. 2006a). Adjustments in movement
mechanics have the potential to reduce torques imposed upon the knee
ligaments (particularly ACL) when landing and during cutting movements
(Myer et al. 2005). Postural control factors, such as degree of knee and hip
flexion upon landing, affect the ability of soft tissues to absorb joint loading
and capacity of relevant muscles (such as hamstrings) to generate protective
forces upon lower limb joints (Lephart et al. 2005). Specific approaches to
movement skills neuromuscular training are discussed in detail in Chapter 3.
The inclusion of high-intensity plyometric training also often differentiates
successful interventions from other studies that did not report significant
reductions in ACL injury incidence (Hewett et al. 2006a). This is likely due to
a combination of factors which are protective for the knee joint. The first of
these is the development of key components of sensorimotor control during
landing and bounding movements, which includes both feed-forward control
and proprioceptive input (Hertel 2008). The second is the development of
eccentric strength and also muscle activation both prior to touchdown and
during the eccentric phase of landing and bounding movements (McBride et
al. 2008). These training effects are likely to facilitate improvements in the
ability to dissipate forces at the knee joint during landing tasks.
The mechanistic connection between trunk, hip and lower limb with
specific reference to knee joint injury has been identified in the literature
(Hewett and Myer 2011). The lumbo-pelvic-hip complex not only provides
proximal control to the lower limb (Mendiguchia et al. 2011) but the position
and motion of the trunk during athletic tasks also influences the stresses
placed upon the knee joint. The latter factor has been specifically implicated
in the mechanism for ACL injury for female athletes (Hewett et al. 2009).
Specific neuromuscular training interventions to develop trunk and hip
control have therefore been proposed as a preventative measure for reducing
knee joint injury (Myer et al. 2008). Various forms of postural balance and
single-leg stabilisation training have previously been shown to have beneficial
impact on knee injury risk factors (Myer et al. 2006b). It has also been
identified that interventions should focus on developing core strength and
lateral stability provided to the trunk in particular (Zazulak et al. 2007). The
reader is referred to Chapter 8 for a summary of training methods to develop
different aspects of core strength and stability.
Figure 10.1 Low box single-leg knee and ankle flexion
It is critical to address any deficits and functional instability for those who
have suffered a previous knee ligament injury, particularly involving the ACL,
in order to protect the player against recurrence of injury to both the
previously injured and ‘healthy’ knee (Orchard et al. 2001). The disruption of
somatosensory function and associated increased risk of re-injury appears to
persist for a long duration for those with a surgically reconstructed ACL and
also those who are ACL-deficient (Ingersoll et al. 2008). It follows that
attention must be given to both recently injured players and also to those
players who have been healthy for an extended period and report full
function. Inhibition of muscle activation is also found in the injured limb of
ACL-deficient and ACL-reconstructed subjects (Ingersoll et al. 2008).
Interventions to help restore sensorimotor function and guard against reinjury should therefore include a combination of training modalities,
including strength training and training modes to develop static postural
balance, dynamic balance and dynamic stabilisation. It is important that
exercises are performed with both limbs, as some of the changes following
injury are also observed in the healthy contralateral limb (Ingersoll et al.
2008).
Patellar tendinopathy
Eccentric strength training is often employed for specific development of
medial quadriceps (VMO) and patella tendon as part of the rehabilitation for
patellar tendinopathy (Zwerver et al. 2007). A range of training modes have
been employed, including controlled eccentric knee flexion movements as well
as rapid drop squats or drop jump landings (Visnes and Barr 2007). Unilateral
single-leg squat protocols have proven efficacy as rehabilitation tool. These
exercises are typically performed on a decline surface, maintaining an upright
posture with minimal forward torso lean and neutral lower limb alignment so
that the supporting knee remains in line with the toes (Visnes and Barr 2007).
A biomechanical analysis identified that employing a decline surface with a
minimum angle of 15 degrees serves to specifically load the patella tendon,
which appears to explain the superior effectiveness of decline squats in
comparison to eccentric squats performed on a flat surface (Zwerver et al.
2007). There does appear to be an optimal range of motion for the exercise –
descending to a knee flexion angle of 60 degrees. Beyond this range, forces
placed upon the patellofemoral joint increase to a greater extent than patellar
tendon forces (Zwerver et al. 2007). In symptomatic athletes, the depth will
initially be governed by pain experienced during the movement – it is
typically recommended to work just into the range where the movement
becomes painful (Visnes and Barr 2007). Within the specific range of motion,
progression can be achieved by adding external load, for example using
dumbbells held at the sides or supported upon the shoulders. Adding a 10kg
load via a backpack was shown to increase knee moment of force by 23 per
cent (Zwerver et al. 2007). It is important, however, that an upright torso
posture is maintained when external loading is added, in order that
appropriate moments of force through the lower limb joints are maintained
during the movement.
Despite the effectiveness generally reported with eccentric training
modalities as a rehabilitation tool for those suffering symptoms of patellar
tendinopathy, data from one study suggest that standard rehabilitation
eccentric training interventions may be less effective for players who are
asymptomatic but exhibit abnormalities on ultrasonograph tendon scans
indicative of increased risk for developing tendinopathy (Fredberg et al. 2008).
Furthermore, the data from studies to date do not indicate that standard
eccentric training modes reduce the initial incidence of signs and symptoms of
patellar tendinopathy. There is therefore no sound evidence to support the use
of the majority of conventional eccentric training modes that are used for
rehabilitation as a means to prevent first-time patellar tendinopathy injury.
It could, however, be speculated that a less conservative approach featuring
higher eccentric loading and more progressive selection of exercise modes
would elicit a greater level of adaptation and might therefore serve a greater
protective effect. An investigation of tendon loading during eccentric training
exercises identified a fluctuating pattern of loading and unloading on the
tendon, which differed from the constant pattern observed during concentric
training (Rees et al. 2009). It has been speculated that these fluctuations in
tendon load, which differentiate eccentric training from conventional training
modes, might be the specific stimulus that elicits remodelling of tendon
structures. In addition, the fluctuations in tendon loading were attributed to
greater difficulty in controlling muscle tension during the eccentric action
(Rees et al. 2009). Specific changes in muscle activation during the eccentric
phase of loaded jumping movements have previously been documented
following training (Cormie et al. 2010a). It could therefore be speculated that
exposure to eccentric loading under appropriate conditions might serve a
protective effect by enhancing the player’s capacity to control muscle
activation and tension during the eccentric phase, thereby sparing the tendon.
It follows that the eccentric training stimulus provided should aim to replicate
the loading conditions and movements encountered during athletic activities.
The hip muscles’ role in providing lumbopelvic stability and controlling
lower limb alignment in single-leg stance and athletic movements, and the
influence on knee joint loads have been identified as critical factors in the
mechanisms of patellar tendinopathy (Boling et al. 2009; Cowan et al. 2009). In
support of this contention, postural balance and dynamic stabilisation training
modes have been shown to reduce the incidence of patellar tendinopathy
among elite female soccer players (Kraemer and Knobloch 2009). Training to
develop strength of lateral trunk and hip abductor muscles should similarly be
a particular area of emphasis, in view of the reported relationship between
reduced lateral trunk strength and patellar tendinopathy (Cowan et al. 2009).
Developing flexibility of muscles of the hip and knee joint likewise would
appear to be an important aspect for the prevention of patellar tendonitis,
given the association found between reduced quadriceps and hamstrings
flexibility scores and incidence of this injury (Witvrouw et al. 2001).
Hamstrings
The increased incidence of hamstring strain injury reported following breaks
of play indicates the importance of a comprehensive warm-up appropriate for
preparing players to perform the activities required in the training session or
match to follow (Brooks et al. 2006). A warm muscle has distinctly different
mechanical properties, particularly with regard to its viscoelasticity. Likewise,
the type of warm-up undertaken can also impact upon neuromuscular
function (Bradley et al. 2007; Little and Williams 2006a). It is important that
this not be neglected for players who enter the play as substitutes, given the
higher rate of injury reported in this scenario (Brooks et al. 2006).
Lumbopelvic posture and stability are also factors that can increase the
strain on the hamstring muscles. A focus of training interventions should be
correcting the anterior pelvic tilt, given the association with hamstring strain
injury (Croisier 2004), particularly the adverse effects this posture appears to
have on activation of the gluteal muscles (Mendiguchia et al. 2012).
Preliminary evidence suggests that interventions to improve lumbopelvic
stability serve a protective role in decreasing the strain on the hamstrings and
thereby reducing the risk of injury (Mendiguchia et al. 2012). It is similarly
suggested that exercises to develop strength and recruitment of the gluteal
muscles should be a focus for preventative interventions as well as
rehabilitation (Mendiguchia et al. 2012). In addition to their role in stabilising
the pelvis from the supporting limb, the extensors of the hip – and the gluteal
muscles in particular – work synergistically with the hamstrings to generate
hip extension and thereby propulsion when running. Decreased activation and
strength of the gluteal muscles following hamstring strain injury has likewise
been implicated in the mechanism for re-injury (Mendiguchia et al. 2012).
There is also a suggestion that ‘stabilisation training’ may serve a role in
reducing rates of re-injury in those with prior hamstring strain injury and
should therefore be included in rehabilitation and preventative interventions
(de Visser et al. 2012).
Strength imbalances are implicated in the incidence of hamstring strain
injury. An investigation that evaluated strength imbalances using isokinetic
strength test measures in soccer players, in particular the ‘mixed ratio’ of
concentric quadriceps versus eccentric hamstring strength, assessed the effects
of corrective strength training on the subsequent rate of hamstring injury
(Croisier et al. 2008). A sub-group of the players identified as having a
strength imbalance when tested at pre-season performed corrective strength
training to normalise the relevant strength ratios. The rate of hamstring strain
injury for these players in the subsequent competition season was reduced to
a level that was in line with players who exhibited no strength imbalance at
baseline (Croisier et al. 2008). This finding supports the efficacy of corrective
training to normalise strength imbalances in reducing hamstring injury risk.
Developing muscular strength offers a means to extend the functional
limits of the hamstrings, in order that there is extra force-generating capacity
in reserve when the muscles’ function is impaired by fatigue. Alongside
strength training, appropriate metabolic conditioning similarly has an
important role in the prevention of fatigue-related hamstring injury by
developing fatigue-resistance (Verral et al. 2005). This is supported by a study
demonstrating significant reductions in hamstring injury following a
programme of preseason training incorporating sport-specific anaerobic
interval training drills (Verral et al. 2005). The success of the training
intervention in reducing hamstring injuries, and number of games missed due
to hamstring injury, was attributed to the adoption of high-intensity sportspecific interval training in place of the submaximal aerobic training emphasis
of previous seasons (Verral et al. 2005).
Although the data are somewhat equivocal, lack of flexibility has been
identified as a risk predisposing soccer players to hamstring muscle strains
(Witvrouw et al. 2003). Reduced flexibility following injury has also been
identified as contributing to the risk of re-injury (Opar et al. 2012). The best
application of flexibility training might therefore be in a corrective function
for those who exhibit reduced hamstring flexibility scores or imbalances
between dominant and non-dominant limbs. Stretches for the hip flexors
should also be considered, in view of the association reported between
reduced flexibility of the hip flexor muscles and increased hamstring strain
incidence in older players (Gabbe et al. 2006). Tightness of the hip flexors may
also contribute to an anterior pelvic tilt, which is likewise associated with
hamstring injury risk (Opar et al. 2012). Static stretching and partner-assisted
flexibility training may be best performed during a cool-down after games
and training or as a stand-alone flexibility training session, in order to avoid
any potential adverse effects on performance (Gamble 2011e).
Figure 10.2 Single-leg hip flexion and extension on domed device
It has been identified that there is a tendency for athletes with a history of
recurrent hamstring injury to show marked strength deficits. These athletes
often show reduced scores with their previously injured limb on a range of
isokinetic measures (particularly eccentric scores and mixed
concentric:eccentric ratio measures) compared to the healthy contralateral
limb (Croisier et al. 2002). It has been demonstrated that these deficits can be
offset via corrective training, and doing so appeared to protect against
sustaining further injury during a 12-month follow-up period (Croisier et al.
2002). Other authors have identified that the optimal angle – that is, knee joint
angle at which the highest isokinetic concentric knee flexor torque was
recorded – is significantly different for the previously injured leg versus the
healthy contralateral limb in athletes with a history of recurrent hamstring
injury (Brockett et al. 2004).
A number of authors suggest that eccentric strengthening exercises in
particular may be important for hamstring strain injury prevention, especially
for those with prior history of hamstring injury (Arnason et al. 2008; Brockett
et al. 2004; Brooks et al. 2006). A potentially critical adaptation associated with
eccentric training, which is not observed with conventional strength training
modes, is eliciting a shift in the length–tension relationship (Brockett et al.
2001). Eccentric training therefore offers a means to correct changes in the
optimal angle observed following injury so that muscle length associated with
peak torque generation is moved closer towards pre-injury values, thereby
helping to restore full function at longer muscle lengths to guard against reinjury (Brockett et al. 2004). Adaptations associated with eccentric training
also serve a persisting protective effect that ameliorates eccentric muscle
damage incurred during other activities undertaken during the period
following the training intervention (Brockett et al. 2001); this phenomenon is
termed the ‘repeated bout effect’.
Injury prevention studies investigating the effects of eccentric training have
typically employed the same corrective strength training modes as used in a
rehabilitation setting. The ‘Nordic hamstrings’ exercise has been employed in
the majority of studies; this exercise is performed in a kneeling position with
the subject’s feet secured by a partner; the subject resists their own
momentum as they fall forwards. There is some evidence that eccentric
training in this form may have a protective effect in reducing hamstring
injuries in team sports players (Arnason et al. 2008; Brooks et al. 2006).
However, the data from other studies are more equivocal and compliance with
this form of training is often reported to be low (Opar et al. 2012).
It should, however, be recognised that conventional rehabilitation
interventions employed following hamstring strain injury have proven to be
ineffective in reducing the reported rates of re-injury over an extended period
(Mendiguchia et al. 2012). In terms of exercise selection, it would equally
appear to be critical that training modes are reflective of relevant movements
in the sport, and that eccentric strength is developed at the required ranges of
motion and muscle lengths. For example, specific development of eccentric
strength at extended hamstring muscle lengths has been recommended
(Croisier et al. 2002). Relevant postures and ranges of motion will include the
critical terminal swing and early stance phases identified within the running
gait cycle (Opar et al. 2012), as well as the locomotion and sports skill
movements that are encountered in the sport. Based on these criteria, the
Nordic hamstring exercise represents a highly nonspecific training mode.
Employing this exercise alone is therefore unlikely to provide the
comprehensive development of strength capabilities that is required, and more
specific training modes should also be considered (Mendiguchia et al. 2012).
For example, variations of the straight-legged deadlift (Figure 10.3) have been
suggested to favour eccentric strength gains at relevant muscle lengths (Opar
et al. 2012).
Adductor muscles
Strength training is recommended to protect against groin injury, in view of
the association reported between adductor muscle weakness and injury
(Engebretsen et al. 2010). In support of this, a pre-season strength training
programme for the adductor muscles was reported to significantly reduce the
incidence of adductor muscle strains in the following season, in comparison to
the rate of injury reported in the previous season (Tyler et al. 2002). Corrective
strength training is recommended particularly for players with a relative
weakness in their adduction versus abduction strength scores (Tyler et al.
2001). Targeted adductor muscle strengthening to correct identified strength
imbalances has accordingly been shown to be effective in decreasing adductor
strain injury incidence (Nicholas and Tyler 2002). Similarly, strength training
for the adductor muscles has been identified as a critical component of
interventions for those with a history of groin pain and injury (Tyler et al.
2002). In terms of exercise selection, given that the adductor muscles are
primarily employed in closed kinetic chain activities, it follows that strength
training for the adductors should similarly feature closed chain exercises.
Figure 10.3 Single-leg dumbbell straight-legged deadlift
Appropriate conditioning is also recommended as a means to protect
against groin injury, based upon the findings that players with lower fitness
scores suffer a greater incidence of groin strain injury (Maffey and Emery
2007). This protective effect of sport-specific conditioning in reducing injury
also appears to show a dose–response relationship – that is, the more training
that players had performed the lower the probability of injury (Emery and
Meeuwisse 2001). Training interventions to specifically develop strengthendurance and increase fatigue-resistance of the adductor muscles might
therefore also be recommended.
Although not a consistent finding, an association has been reported
between impaired adductor muscle flexibility and risk of adductor muscle
strain. Baseline scores of passive hip range of motion in abduction were found
to be associated with subsequent incidence of adductor muscle injury in
soccer players (Arnason et al. 2004). This association was not found in a study
of professional ice hockey players, suggesting the influence of adductor
muscle flexibility on injury risk may depend upon the sport (Tyler et al. 2001).
Flexibility training is therefore recommended for ‘at risk’ sports such as
soccer, and it may also be prudent to include these exercises for players in
other sports.
As deficits in lumbopelvic stability are identified as a risk factor for groin
strain injury, it is also recommended that training to develop lumbopelvic
stability should be included in preventative training interventions. Corrective
training to develop recruitment and function of the deep lumbar postural
muscles and muscles of the hip complex is recommended, particularly for
those with a history of groin pain and adductor strain injury (Maffey and
Emery 2007). The reader is referred to Chapter 8 for information about specific
training interventions.
Figure 10.4 Side bridge ‘wipers’ on domed device
Lumbar spine
Team sports players in particular have a need for both strength and endurance
for the muscles that stabilise the spine in all three planes of motion (Barr et al.
2005; Leetun et al. 2004). Endurance rather than absolute strength of trunk
muscles has been identified as being the most decisive factor with regard to
low back pain incidence (McGill 2007b). Fundamentally, the postural muscles
are designed to operate isometrically to provide stability to the lumbar spine.
Accordingly, it has been identified that training modes that incorporate a
static hold are found to be most effective in eliciting gains in cross-sectional
area of deep lumbar stabilisers (multifidus) in patients with chronic low back
pain (Danneels et al. 2001).
The muscles of the hip complex serve a major role in all dynamic activities
performed in an upright stance (Nadler et al. 2000). The hip muscles are
involved particularly in stabilising the pelvis during single-leg stance and the
generation and transmission of forces from lower limb(s) to the spine.
Correcting hip abductor strength imbalances via a core strengthening
programme shows the potential to reduce subsequent lower back pain
incidence (Nadler et al. 2002). Isometric hip external rotation strength was
identified as the single best predictor of lower back and lower extremity
injury incidence in collegiate athletes (Leetun et al. 2004). The importance of
hip muscle function and the co-ordination between motion at the hips, pelvis
and lumbar spine during throwing and striking sports skill movements has
also been highlighted with respect to low back pain and injury (Harris-Hayes
et al. 2009).
A critical aspect of injury prevention is neuromuscular and movement skills
training to reinforce safe and ‘spine-sparing’ postures and movement patterns.
A ‘neutral’ spine alignment is the most advantageous from the point of view
of stability – when in a flexed position the lumbar spine is less able to resist
both compressive and shear forces (McGill 2007b). Maintaining a neutral spine
posture when performing athletic tasks is therefore beneficial for lumbar spine
stability and helping to maintain the joint structures and connective tissues
concerned within their failure limits. Accordingly, a key aspect of spinesparing movement strategies is that motion occurs predominantly from the
hips, rather than moving at the lumbar spine. Adopting these ‘safe’ postures
and movement strategies not only spares the spine but also often facilitates
superior athletic performance (McGill 2007b).
Corrective neuromuscular training to develop strength and recruitment of
the deep postural muscles is also likely to be necessary for players with a
history of lumbar spine pain and injury, based upon the finding that low back
pain is often accompanied by disrupted motor patterns of various stabilising
muscles (Rogers 2006). Similarly, a common finding is that deep lumbar spine
stabiliser muscles are atrophied in individuals with chronic lower back pain
(Barr et al. 2005). Importantly, this atrophy does appear to be reversible with
appropriate training intervention, with associated improvements in low back
pain symptoms (Hides et al. 2001). Individuals with chronic lower back pain
also exhibit impaired neuromuscular feedback and delayed muscle reaction,
which is accompanied by reduced capacity to sense the orientation of their
spine and pelvis (Barr et al. 2005). The importance of ‘proprioceptive’ training
to develop sensorimotor control has therefore been highlighted with respect to
maintaining lumbar spine stability and reducing risk of pain and injury
(Borghuis et al. 2008).
Specific training aimed at addressing the various functional deficits
associated with low back pain and injury are likely to serve a protective
function in guarding against both first-time incidence of injury, and
recurrence injury in those with a history of low back pain. This should include
developing strength and particularly endurance of muscles that provide
lumbopelvic stability, addressing hip muscle weakness and imbalances, and
developing proprioceptive awareness of lumbar posture and positioning of the
pelvis (Rogers 2006). The various systems and muscles that provide stability to
the lumbo-pelvic-hip complex work in different combinations depending on
the posture and movement; a variety of exercises are therefore required (Axler
and McGill 1997). Progressions should include exercises performed in standing
postures and involving weight-bearing closed chain movements, in order to
integrate the hip musculature and help develop balance and proprioception.
The reader is referred to Chapter 8 for a full description of training
approaches to develop lumbopelvic stability.
Neuromuscular and movement skills training that reinforces safe lumbar
spine posture and emphasises moving the torso from the hips should be
included in players’ preparation (Barr et al. 2005; McGill 2007b). Maintaining
the functional range of motion of muscles that cross the hip is also key to
allowing these movement strategies and postures to be adopted. It follows that
flexibility training for the hip and lower limb is another important aspect of
training to help prevent low back pain and injury.
Shoulder complex
Acute shoulder injury
There is a suggestion of a fatigue element in the incidence of contact shoulder
injuries in collision sports, based on the observation that injuries are
commonly sustained during the latter stages of matches and training sessions
(Headey et al. 2007). Similarly, transient reductions in function associated
with microtrauma resulting from repeated collisions may also contribute to
this finding in the case of matches and contact training sessions (Takarada
2003). One implication of this finding is that coaches in collision sports must
allow for this by scheduling adequate recovery time following competitive
matches and contact skills practices to guard against cumulative damage that
may decrease function and predispose the player to more serious shoulder
injury. Training interventions can also increase fatigue resistance and reduce
the degree of muscle damage following strenuous physical exertion.
Appropriate physical preparation, including strength training and contact
skills conditioning, therefore has an important role in protecting against
muscle damage, improving recovery of function and offsetting the effects of
fatigue (Takarada 2003).
Targeted strength training interventions to develop strength and integrated
function of the muscles that stabilise the joints of the shoulder girdle offers a
means to enhance the structural integrity and failure limits of the shoulder. As
a consequence of the high degree of mobility at the shoulder complex, it is
heavily reliant upon the active stability provided by the integrated function of
various muscles. As the majority of the range of motion during movement
originates at the glenohumeral joint and from the articulation of the scapula
and thorax (Myers and Oyama 2008), it follows that these areas should be the
focus for training interventions. Both strength and strength-endurance should
be addressed, in view of the observed influence of fatigue on shoulder injury
incidence (Headey et al. 2007).
The optimal approach to preventive strength training for the shoulder
complex will be in part dependent on the profile of the player. For example, if
a particular imbalance has been identified, isolated exercises to strengthen
particular muscles will be warranted (Beneka et al. 2006). If no imbalance has
been identified, or pre-existing imbalances have been resolved, the use of
more complex exercises has been advocated (Malliou et al. 2004). Such
exercises allow muscles of the shoulder and upper limb to be recruited in a
more integrated fashion (enabling sport-specific movements to be
incorporated) and also facilitate greater gains in functional strength
(Giannakopoulos et al. 2004). However, ongoing targeted strengthening for
rotator cuff and scapula stabilisers should not be neglected for players in
sports that are known to be particularly prone to shoulder injury (Gamble
2004b).
Resistance in the form of either free weights (such as dumbbells) or cable
machines is generally preferable for these exercises as they avoid the adverse
length–tension relationship associated with resistance bands or tubing, as well
as providing greater ease of progressing load. Exercises for the scapula
stabilisers should include rowing and pulling exercises that focus on retracting
and adducting the scapula – for example, cable and dumbbell rows, cable lat
pulldown exercise, and both standard and supine variations of the pull up – as
well as exercises that focus on controlled scapular protraction, such as the
‘push up plus’ and dumbbell pull over exercises (Escamilla et al. 2009). Each of
the four rotator cuff muscles is activated to varying degrees depending on the
position of the upper limb and the constraints of the movement being
performed (Decker et al. 2003; Takeda et al. 2002). It follows that exercise
selection should reflect the movements and the loading conditions
encountered during matches.
Given the high rate of re-injury and the severity of recurrent shoulder
injuries it is critical that any residual deficits in function and sensorimotor
control are addressed for players who have suffered previous shoulder injury
(Headey et al. 2007). The reduced mechanical stability provided to the
shoulder following traumatic injury, for example due to joint capsule and
ligamentous laxity, increases the importance of active stabilisation but also
poses challenges for proprioceptive function (Myers and Oyama 2008). It is
therefore vital that sensorimotor training interventions are employed to help
restore proprioceptive function in order to address the deficits in
neuromuscular control and functional stability observed with players with
previous shoulder injury. Prescription of specific exercises is discussed in the
following section.
Overuse injuries of the shoulder complex
Chronic shoulder pain and injury are strongly associated with muscle
imbalances or deficits in function of the rotator cuff of muscles that stabilise
the glenohumeral joint and the muscles that control the articulation between
the scapula and the thorax. For example, a relative weakness of external
rotators is associated with overuse shoulder injury and is particularly
prevalent among players in overhead sports (Wang and Cochrane 2001).
Targeted strength training for the muscles that act on the glenohumeral joint
and stabilise the scapula is therefore required, particularly for players in
throwing and striking sports, to help avoid developing shoulder pain and
overuse injury (Wagner 2003). This should include interventions to help
correct or prevent the development of deficits in strength and strengthendurance that are characteristically observed in these sports.
Assessing the strength ratio between internal and external rotators is
therefore a recommended starting point when addressing balance between
muscles of the glenohumeral joint (Beneka et al. 2006). This assessment can be
undertaken using an isokinetic device if available (Giannakopoulos et al. 2004)
or dumbbells if not (Beneka et al. 2006); in either case, both internal and
external rotators are assessed in a position with the upper arm abducted at 90
degrees. Given that the external rotators act predominantly in an eccentric
fashion when stabilising the glenohumeral joint during throwing and striking
movements, it follows that eccentric strength or torque measurements are
most relevant for these muscles (Niederbracht et al. 2008). The strength ratio
expressed between internal rotators’ concentric strength versus eccentric
strength of external rotators is therefore suggested to be more valid. As
alluded to previously, improving eccentric strength scores of the external
rotators in relation to concentric strength of the internal rotators would
appear to be the more critical issue (Niederbracht et al. 2008). Concentric
strength improvements of external rotators are not always shown in following
injury prevention training interventions. However, regardless of any lack of
changes in concentric torque, eccentric strength measures are shown to
improve in response to specific strength training for the external rotator
muscles (Niederbracht et al. 2008).
Once identified, training modes can be selected to address rotator cuff
muscle imbalances. A number of different exercises have been identified that
elicit significant activation of each of the four rotator cuff muscles either alone
or in combination (Escamilla et al. 2009). Isolated exercises with dumbbells,
isokinetic training and multi-joint upper-body strength training exercises all
have application to improving external versus internal peak torque ratios
(Malliou et al. 2004). Once isolated exercises for specific development of
rotator cuff muscles have been introduced, more complex exercises can be
included in players’ training which allow greater force development
(Giannakopoulos et al. 2004). The muscles that control the articulation
between the scapula and the thorax serve a crucial role in helping to achieve
an optimal position and orientation of the socket in which the head of the
humerus sits (Behnke 2001). A continuing focus on these muscles in players’
physical development is therefore critical in order to maintain joint integrity
and avoid impingement at the glenohumeral joint.
Functional problems with the shoulder complex are not always a result of
activity: poor posture can also place the scapulae in a protracted position,
creating a ‘rounded’ shoulder posture. Errors in physical preparation can have
a similar effect on scapula position: unbalanced development of anterior
(particularly chest) muscles can result in a protracted resting posture. Strength
training for the middle and lower back muscles (rhomboids, middle and lower
trapezius) that retract the scapulae can also serve an important role in
correcting suboptimal postural traits. Appropriate exercises can strengthen
these middle back muscles while actively stretching the shortened anterior
muscles, helping to bring the resting position of the scapula back towards the
desired position.
An impaired sense of scapula position and reduced ability to control the
motion of the scapula about the wall of the thorax is a common finding
among players who experience shoulder pain and injury in sports that involve
repetitive throwing or striking (Wang and Cochrane 2001). This may be
accompanied by reduced function affecting not only the rotator cuff muscles
but also the prime movers of the glenohumeral joint. The changes in
sensorimotor control observed with overuse shoulder injuries are attributed to
inhibition effects that result from the pain and the impingement that is often
associated with these conditions (Myers and Oyama 2008). Strength training
offers a means to improve sensorimotor control and help to restore pain-free
function. A range of exercises have been recommended for scapula
stabilisation, including dumbbell and cable exercises (Brummitt and Meira
2006), which can be employed to develop strength and improve the capacity to
control scapula positioning during movement. There will also be a need for
corrective proprioceptive training for those athletes who exhibit suboptimal
scapulo-humeral rhythm or shoulder repositioning test scores during
screening.
For overhead striking (as in volleyball) and throwing sports (baseball,
softball, team handball) in particular, flexibility training to offset
characteristic changes in internal versus external rotation range of motion
appears warranted (Lintner et al. 2007). The common profile of baseball
pitchers is for them to exhibit reduced internal rotation at the shoulder
alongside increased range in external rotation (Mullaney et al. 2005). This is
believed to be a consequence of repeatedly performing the throwing action
during practices and games, often spanning a period of many years. Whereas
the increased external rotation appears to be a structural (that is, bony)
adaptation in the orientation of the humeral head and as such a relatively
permanent adaptation, the reduction in internal rotation does appear to be
modifiable. Professional baseball pitchers who had undertaken a programme
of flexibility training targeted at addressing posterior capsule tightness over a
prolonged period scored significantly higher on internal rotation range of
motion measured on their dominant (throwing) arm (Lintner et al. 2007).
Figure 10.5 Prone dumbbell external rotation
Figure 10.6 Prone dumbbell lateral raise
Figure 10.7 Alternate arm cable reverse fly
Figure 10.8 Cable diagonal pulley
Summary
The paucity of well-controlled injury studies make definitive
recommendations with regard to evidence-based injury prevention training
difficult, particularly in the case of muscle injuries such as hamstring strains
(Peterson and Holmich 2005). In the absence of such studies, it is necessary to
rely upon what is known about specific injury mechanisms and relevant
modifiable risk factors for the particular injury.
Common themes include:
•
Addressing functional stability by improving proprioception and
neuromuscular control;
• Incorporating all parts of the lower limb kinetic chain – recognising the role
of the hip musculature in providing proximal control to the lower limb and
absorbing landing forces (Hewett et al. 2006a);
• Increasing muscle strength and correcting strength imbalances in order to
increase in mechanical stability provided to a joint;
• Addressing muscle tightness and imbalances in mobility and flexibility via
targeted flexibility training where deficits are identified.
In order to be most effective, the design of an injury prevention training
intervention should not only be specific to the injury but also to the sport
(Bahr and Krosshaug 2005). Practically, this means that exercise prescription
should progress to exercises that reflect the specific conditions of the sport.
11
PLANNING AND SCHEDULING
Periodisation of training
Introduction
Training variation is fundamental to successful training prescription (Fleck
1999; Stone et al. 2000b; Willoughby 1993). Periodisation offers a framework
for planned and systematic variation of training parameters (Brown and
Greenwood 2005; Plisk and Stone 2003; Rhea et al. 2002; Stone et al. 2000b).
Accordingly, it has been established that periodised training is able to elicit
improved training responses in comparison to training groups with no
variation in training load (Fleck 1999; Stone et al. 2000b; Willoughby 1993).
The consensus is therefore that periodised training offers superior
development of strength, power, body composition and other performance
variables (Fleck 1999; Stone et al. 1999a, 1999b, 2000b; Wathen et al. 2000;
Willoughby 1993). Despite this there are very limited research data upon
which to base decisions regarding the best approach to periodisation,
particularly in the case of athlete populations (Fleck 1999; Cissik et al. 2008).
The choice of periodisation schemes is therefore likely to be largely dictated
by what is most appropriate for the competition calendar involved in the
particular sport and what other training and technical practices the athlete is
concurrently performing (Wathen et al. 2000).
In view of this, unique challenges are faced when attempting to apply
periodisation to training design in team sports. Team sports players are
required to perform high volumes of technical and/or tactical training, team
practices and competitive matches. As a result, successful application of
periodised training design for team sports requires considerable planning and
skill (Gamble 2004b). Indeed there are numerous complications that represent
an obstacle to effective application of periodised training in most team sports.
Despite these considerations, training variation provided by periodisation
remains vitally important for team sports athletes. It follows that the approach
to periodisation should be specific to the demands of the particular team sport,
including the length of the competitive season and the number and frequency
of fixtures involved. Selection of periodisation methods for different training
mesocycles throughout the year should also reflect the needs of the respective
phase of training (Plisk and Stone 2003).
Training variation
Training variation is acknowledged as serving a critical function in successful
training prescription (Fleck 1999; Stone et al. 2000b; Willoughby 1993).
According to either general adaptation syndrome (Selye 1956) or the more
recent fitness–fatigue theory (Chiu and Barnes 2003), sustained exposure to
the same training stimulus over time will fail to elicit further adaptation, and
in time may lead to diminished performance (Wathen et al. 2000). One aspect
of training variation is therefore avoiding plateaus in training adaptation or
‘maladaptation’ (negative impact on performance resulting from unplanned
overreaching or overtraining).
Another issue when planning athletes’ training is that only two or three
training goals can be emphasised at any one time (Zatsiorsky and Kraemer
2006). This is the case particularly with conflicting training goals that involve
opposite hormonal responses (such as catabolic versus anabolic) and
neuromuscular fatigue that interfere with training adaptation. Those sports
that require a variety of training goals require that training is varied in a
systematic way in order that different training goals are accounted for during
different phases in the athlete’s training year.
The degree of training variation required is also likely to be specific to the
training experience of the individual (Plisk and Stone 2003). More basic
periodisation schemes that involve less variety in training parameters are
sufficient for younger athletes or those who do not have a long training
history (Bompa 2000; Kraemer and Fleck 2005; Plisk and Stone 2003). This is
not the case for more advanced athletes.
Periodisation of training
Periodisation was developed with the aim of manipulating the process of
training adaptation, primarily in an effort to avoid the maladaptation phase
and combat the risk of non-functional over-reaching or the more chronic state
of overtraining or ‘unexplained underperformance syndrome’ (Wathen et al.
2000; Brown and Greenwood 2005). Periodisation offers a framework for
planned and systematic variation of training prescribed to vary the training
stimulus at regular intervals in order to prevent plateaus in training responses
(Brown and Greenwood 2005; Plisk and Stone 2003; Rhea et al. 2002; Stone et
al. 2000b).
Accordingly, it has been established that periodised training is able to elicit
improved training responses in comparison to training groups with no
variation in training load (Fleck 1999; Stone et al. 2000b; Willoughby 1993).
However, very few studies of sufficient length assessing the effects of different
approaches to periodised planning have been published (Fleck 1999). As such
there are insufficient data upon which to base decisions when selecting the
best approach to periodisation in order to plan athletes’ training (Cissik et al.
2008).
One of the primary considerations when selecting the most appropriate
periodisation scheme upon which to plan the training year is the competition
calendar for the particular sport (Wathen et al. 2000). Another complication
when scheduling athletes’ training is the interaction of concurrent training
and technical and/or tactical practices performed in the sport. In addition to
scheduling concerns, the number and variety of training goals demanded in
the sport are another key consideration.
Scheduling and transfer of training effects
In addition to avoiding potential negative effects of training monotony, use of
periodisation schemes allows planning of training prescription to prioritise
selected training goals at particular times in the training year. Periodisation
and appropriate scheduling also offer the strength and conditioning specialist
the facility to take advantage of the residual effects of preceding training
cycles (Zatsiorsky and Kraemer 2006). Essentially, preceding phases of
training can be used to ‘potentiate’ or enhance the athlete’s response to the
particular training prescribed in subsequent cycles. This ‘superimposition’ of
training effects may be achieved via a coherent progression of training
prescription during successive training cycles, and in particular the selection
of training modes employed for different aspects of physical preparation. This
is illustrated in Figure 11.1.
Periodising intensity, volume and content of training
prescribed
In the traditional periodisation models, the training year or macrocycle is
divided into an initial general preparation phase ‘GPP’, followed by special
preparation phase(s) ‘SPP’ and culminating in the competition phase. The GPP
is typically preceded by a period of active rest following the previous
competition season and each phase within the training cycle may be separated
and subdivided with ‘transition’ cycles (Wathen et al. 2000). The training
goals for each cycle classically follow a particular sequence (Zatsiorsky and
Kraemer 2006).
The goals during the general preparation phase are classically hypertrophy
and/or strength-endurance and base metabolic conditioning to provide a
foundation for the subsequent training phases in the year. Training goals then
sequentially progress during the special preparation phase from general
strength to strength/power and there is a shift to more intensive metabolic
conditioning. The training goals that predominate during the competition
phase will depend upon the sport; however, strength training is typically
oriented towards power and power-endurance and metabolic conditioning
becoming highly specific to the bioenergetics of the sport.
In accordance with the training goals for the respective phases of training,
the early cycles in the training year or ‘macrocycle’ during the general
preparation phase are characterised by higher training volumes and lower
intensities (Wathen et al. 2000). Classically, as the training year progresses
through the special preparation phase and into the competition phase, training
intensity is increased with corresponding decreases in training volume.
Whatever the periodisation scheme employed, intensity and volume will
broadly show this diverging pattern (intensity progressively increasing and
volume progressively decreasing) over the course of the training macrocycle.
Another factor that comes into play during competition cycles is tapering of
training frequency and volume for critical phases in the competition calendar
to allow residual fatigue effects to subside in order that training effects can be
fully expressed in the athlete’s competition performance (Zatsiorsky and
Kraemer 2006).
Periodic changes in exercise selection and conditioning modes are
important in order to systematically change the training stimulus and thereby
facilitate continued training adaptation (Zatsiorsky and Kraemer 2006). The
classical model for periodised planning is for training modes to feature a
progressive shift from ‘general’ training modes during general preparation
cycles to increasingly ‘specific’ training modes, particularly as the athlete
approaches key phases in the competition period. Accordingly, the general
preparation phase is classically characterised by general strength training
exercises and relatively nonspecific metabolic conditioning modes including
cross training. The special preparation phase in turn features a gradual
progression towards the sport-specific strength training exercise selection and
metabolic conditioning modes that characterise the competition phase. This
sequential shift towards the most specific strength training movements and
conditioning modes is designed to translate the general or ‘non-specific’
strength qualities and conditioning base developed during earlier training
cycles into sport-specific strength and fitness as the athlete enters the
competition phase (Zatsiorsky and Kraemer 2006).
Figure 11.1 Periodisation of exercise selection schematic
Approaching periodisation
When planning athletes’ training it is customary to divide the ‘macrocycle’
(training year or biennial or quadrennial cycle in the case of Olympic sports)
into smaller blocks called ‘mesocycles’ (Zatsiorsky and Kraemer 2006). Within
each mesocycle are smaller blocks of time known as microcycles, which
typically comprise a week or two-week block. Periodisation of training should
consider planned variation and scheduling at levels from macrocycle, to
mesocycle and microcycle. For example, planning at the level of the macrocycle must consider the key dates in the competition season. Planning at
microcycle level concerns not only structuring individual sessions to meet the
goals of particular phases of the training mesocycle, but also scheduling the
training week to account for the respective demands of competitive matches,
different training sessions and technical and/or tactical practices. Scheduling
each training microcycle also requires consideration of potential negative
interaction between conflicting forms of training – for example aerobic
conditioning and strength/power training.
Periodisation schemes
A variety of periodisation models have been described in the literature. A
brief outline of the different categories of periodisation schemes that are
employed in various sports is presented here.
Linear periodisation
The classic ‘linear’ format for training periodisation is characterised by
gradual increases in training intensity between successive mesocycles, with
simultaneous reductions in training volumes. This progression culminates in a
competition cycle, which is scheduled to coincide with one or more major
competitions in the calendar and designed to allow the athlete to arrive at
these competitions in peak physical condition (Wathen et al. 2000). Reverse
periodisation approaches have also been employed which feature the opposite
pattern – that is, high intensity and low volume employed at the outset, with
progressive decrease in intensity and increase in volume thereafter,
culminating in low intensity and high training volume. The reverse linear
periodisation approach is, however, consistently found to produce inferior
results to standard linear periodisation and other approaches (Prestes et al.
2009; Rhea et al. 2002).
With the classical linear periodisation format there is considerable variation
in training prescription between consecutive phases in the training year, but
little or no variation within each training block. Hence it is suggested that this
approach may not provide sufficient variation in the training stimulus for
athletes with extensive training experience. Modifications to the traditional
linear periodisation approach have been employed that feature condensed
training mesocycles, which serves to provide more frequent variation of
training parameters. One example is the eight-week condensed linear model
described by Allerheiligen and colleagues (2003) featuring condensed twoweek mesocycles performed in series. A recent study successfully
implemented another modified and condensed linear periodisation scheme
that employed weekly alterations in training parameters, following the
classical diverging pattern of progressively increasing intensity with
concurrent reductions in volume (Prestes et al. 2009).
Block periodisation
This modified approach to periodisation was proposed as a solution to
perceived shortcomings of the traditional linear approach in the context of the
demands of modern high-performance sport, and in particular the challenges
posed by the mixture of different forms of training performed by athletes in
many sports (Issurin 2010). The rationale for block periodisation is based on
the contention that different forms of training will produce conflicting
physiological and endocrine responses, and as such attempting to perform
‘mixed training’ in combination for a prolonged period would elicit excessive
fatigue and provide a suboptimal training stimulus over time. This contention
has been challenged by other authors (Kiely 2010).
The proposed solution that is encompassed by the block periodisation
approach is to adopt a more ‘unidirectional’ training emphasis within each
training mesocycle. Specifically, the different forms of training performed
concurrently by the athlete at any time should be restricted to only a minimal
number. This approach essentially proposes a short (one- to three-week)
concentrated block featuring a high volume of targeted training aimed at
developing only one or two selected abilities, which is typically followed by a
taper to prepare the athlete for an identified competition and a period of
active recovery prior to the next intensive training cycle (Issurin 2010).
Nonlinear periodisation
Nonlinear or ‘undulating’ periodisation schemes involve variation in intensity
and volume within a training microcycle, in addition to variation between
mesocycles (Wathen et al. 2000). Nonlinear undulating periodisation is
suggested to be more appropriate for highly trained athletes due to the greater
level of training variation (both within and between training cycles) afforded
by this approach (Monteiro et al. 2009). This approach is also devised to keep
the athlete close to their peak for multiple competitions spanning an extended
period. The variation between workouts within each micro-cycle also allows
for multiple training goals to be addressed simultaneously (Zatsiorsky and
Kraemer 2006).
Both daily and weekly undulating periodisation schemes are described in
the literature and employed in the field (Buford et al. 2007). Daily undulating
periodisation involves variation on a daily basis so that the training stimulus
provided by each session within the training week is markedly different (Rhea
et al. 2003). Weekly undulating periodisation involves large fluctuations in
training intensity prescribed between consecutive weeks; however, the
programming of sessions within each week remains consistent. For those with
less training experience there is some evidence that the large fluctuations in
training intensity that feature in the weekly undulating periodisation
approach may limit the effectiveness of this approach due to the muscle
soreness caused (Apel et al. 2011). In this case, the traditional linear approach
appears to be more effective and might therefore be more suitable for younger
or less experienced players, depending on their training history.
Summated mesocycles approach
Variations of the summated mesocycles method have been successfully
applied in both rugby union and rugby league football (Baker 1998). This
format involves a step-like increase in volume load (the product of training
volume multiplied by training intensity) followed by a pronounced taper.
Classically, the summated microcycles format operates around a four-week
cycle, with the final week of the four-week cycle acting as an unloading week
with considerably decreased volume load. This is designed to accommodate
the time course of physiological processes underlying training adaptations and
fatigue effects (Plisk and Stone 2003). These ‘mini-cycles’ are repeated in series
at greater or lesser relative intensities. This basic pattern can therefore be
employed sequentially to create a wave-like pattern in lifting intensity and
training volume.
Use of periodisation in professional team sports
Strength and conditioning coaches working in a multitude of team sports at
various levels report adopting a periodised approach to their programme
design. The use of periodisation was indicated by the vast majority of Division
One collegiate strength and conditioning coaches in the United States
responding to a survey of their methods (Durell et al. 2003). Similar surveys of
professional North American team sports reported comparable use of
periodised training design (Ebben and Blackard 2001; Ebben et al. 2004, 2005;
Simenz et al. 2005). These included National Basketball Association (90 per
cent of respondents using periodised programmes) (Simenz et al. 2005),
National Hockey League (91.3 per cent using periodisation) (Ebben et al. 2004),
and Major League baseball (83.4 per cent) (Ebben et al. 2005).
National Football League coaches reported by far the lowest use of
periodisation models (69 per cent) (Ebben and Blackard 2001). This may be a
result of the contact nature of the sport. On the issue of training periodisation,
one coach was quoted as saying ‘Weight training in football is different than
any other sport. When you have them healthy, (you) train them’ (Ebben and
Blackard 2001). The fact that the data collection for this study was notably
earlier (1997–98) than the other respective surveys may also have played a
part. This may in turn explain the relatively greater use of ‘high-intensity
training’ methods (19 per cent) by the coaches in the sample (Ebben and
Blackard 2001), which was enjoying relative popularity at the time.
Such difficulties as injuries and residual fatigue underline the unique
challenges of designing periodised programmes for team sports athletes,
particularly in the case of contact sports. Despite these considerations,
training variation remains vitally important for team sports athletes. This is
important to alleviate the monotony that can otherwise affect compliance
throughout a long season of training and competition (Wathen et al. 2000).
Taking player motivation aside, it is counterproductive and even harmful to
train in the same way for extended periods. Short-term training studies
consistently show training programmes that incorporate periodised training
variation elicit superior results (Stone et al. 2000b; Willoughby 1993). Solutions
to these complications must therefore be sought to enable periodised training
to be incorporated into athletes’ physical preparation in a given sport.
Challenges and practical solutions for periodised team
sports training
Extended season of competition
A major obstacle for coaches working in seasonal team sports is the frequent
matches and extended competition period involved. The classical periodisation
models for planned training variation were developed for the competitive
season in track and field athletics (Plisk and Stone 2003). As a result, the
classical linear periodised format features extended training cycles, designed
to progressively prepare the athlete for one or two major championships in
the year (Wathen et al. 2000).
The playing season for sports such as soccer and rugby union can span in
excess of 35 weeks, particularly in Europe. If coaches were to follow the
classic model, training would taper considerably for the duration of the
competition phase. This is clearly counterproductive for most team sports
(Baker 1998; Hoffman and Kang 2003). It has been identified that following
such restrictive competition phase repetition schemes may lead to excessive
losses in lean body mass during the season, which is unfavourable for most
power sports (Allerheiligen 2003). Given this requirement to continue regular
training over many months, achieving the necessary training variation
represents a sizeable challenge.
It is vital that strength training is maintained in-season to prevent
significant losses in strength, power and lean body mass (Allerheiligen 2003;
Baker 1998). Periodisation schemes for in-season training will necessarily
differ from those applied during off-season and pre-season training cycles.
This will be discussed in greater detail later in the chapter.
Multiple training goals
Team sports require several disparate training goals. These can include, but
are not limited to: hypertrophy, maximum strength, explosive power,
metabolic conditioning and injury prevention (Gamble 2004b). Multiple and
often conflicting training goals must therefore be addressed in the course of
the training plan. In view of this, there is a need for planned variations in the
training programme to systematically shift the emphasis to promote these
different training effects at different points in the players’ preparation.
Due to the need to maintain different neuromuscular and metabolic
training goals as well as cater for technical and tactical practice, some
periodisation strategies may not be appropriate for a given sport. An example
of a periodisation scheme that appears less suited to the multiple training
goals associated with many team sports is the conjugate periodisation model
(Plisk and Stone 2003). This is an advanced approach that aims to exploit
fitness and fatigue after-effects by consecutive overload cycles, alternately
stressing one motor quality (for example, strength) for a period then switching
to overload another motor quality (such as speed) for the subsequent training
cycle (Plisk and Stone 2003). Two main training goals are hence typically
coupled in this approach. During the overload phase for the other motor
quality in the couple (strength), a low volume maintenance programme is
undertaken for the motor quality not being emphasised (speed) (Plisk and
Stone 2003). These overload cycles are alternated in series. The greater
number of training goals required by many team sports than the two motor
qualities typically addressed in this periodisation format would obviously
make the application of this approach problematic.
It has been suggested that undulating, ‘non-linear’, periodised approaches
are more viable when planning the training year for team sports (Wathen et
al. 2000). The rationale for this is that such periodisation strategies allow for
more variation in both training intensity and volume, both within and
between training cycles. As such multiple training goals can be emphasised in
each training microcycle (Zatsiorsky and Kraemer 2006). However, at some
phases of the training year, in particular the off-season and pre-season,
sequential approaches similar to the classical linear periodisation model may
still have merit. This is explored further in a later section.
Interaction between different forms of training
When programming strength training, coaches must also take account of the
interaction of the different forms of training that are undertaken concurrently
within the training week by team sports players (Gamble 2004b). From this
viewpoint, the physical activity involved in technical and/or tactical sessions
and team practices should also be considered. Specifically, a major
consideration is the high volume of metabolic conditioning undertaken
alongside strength training and power and speed development in many team
sports. It has been documented that a prior bout of endurance exercise in the
training day is shown to impair an athlete’s ability to perform strength
training (Kraemer et al. 1995; Leveritt and Abernethy 1999). After performing
a conditioning session, players are reportedly not able to complete the same
number of repetitions with a given load that they are capable of without
having previously performed endurance exercise (Leveritt and Abernethy
1999).
These interference effects are also associated with conflicting hormonal
responses to strength versus endurance training, which may blunt the
response to strength and power training. When strength training is performed
in the same day following endurance training, training outcomes with respect
to power indices in particular are shown to be affected (Kraemer et al. 1995). It
therefore appears that strength and power training outcomes that are
associated with greater neuromuscular co-ordination demands may be most
susceptible to such interference effects.
Time constraints imposed by concurrent technical and
tactical training
Given the time constraints imposed by the high volumes of team practices and
other skill training common to all professional team sports, the time-efficiency
of physical preparation is paramount. As the playing season approaches, focus
inevitably shifts to tactical aspects – with a greater number of team practices
to prepare for the forthcoming fixtures (Hedrick 2002; Wathen et al. 2000).
During the season, the need to maximise the effectiveness of what limited
training time is available is greater still.
The issue of limited training time may be addressed by optimising the timeefficiency of the training that is performed. A useful strategy is to incorporate
different elements in order to combine practice and physiological training
aspects in a single session. Particularly in-season, speed development and
agility work can be included in team practice sessions (Wathen et al. 2000).
Similarly, plyometric work can be incorporated into strength training sessions
– for instance by employing complex training methods.
A good example of combined physiological and technical training is the use
of game-related methods for metabolic conditioning (Gamble 2007b). The skill
element involved encourages coaches to continue metabolic conditioning via
the use of conditioning games when the training emphasis shifts to skills
practice and game strategy (Gamble 2004a). Continuing metabolic
conditioning in this form during the playing season is likely to allow
cardiorespiratory endurance to be better maintained in-season.
Impact of physical stresses from games
When planning training during competition periods, allowances will
inevitably need to be made for players’ recovery after each match. Particularly
in the days following games, this need to allow the players’ bodies to recover
is likely to limit the intensity and volume of physical training they are able to
perform. As such there is the potential for the high volumes of physically
demanding practice sessions and competitive games during the season to
result in players losing muscle mass during the playing season (Allerheiligen
2003).
In the case of contact sports in particular, consideration must also be given
to the physical stresses that result from violent bodily contact with opponents
and the playing surface during both practices and matches. As a consequence
muscle tissue damage incurred particularly during the playing season may
compromise the quantity and content of strength training that players are able
to undertake, potentially to the extent that strength and power levels may be
diminished over time (Hoffman and Kang 2003).
Scheduling of training in-season and during late pre-season when
competitive matches are being played should take appropriate measures to
tailor training sessions to the players’ physical status. In the day(s)
immediately following the game, strength training will necessarily be limited
to light recovery workouts, implemented alongside acute recovery practices.
Similarly, the strength and conditioning coach should be prepared to modify
the workout scheduled for a given day in the event that a player reports to
training suffering from excessive residual fatigue or with a diagnosed acute
injury that will impair their ability to perform the particular session set on
that day (Plisk and Stone 2003).
Practical application of periodised training for a team
sports season
As discussed earlier in the chapter, the degree of variation in training loads
and volumes will depend on the age and experience of the player. Elite players
are capable of tolerating higher training stress – hence training intensity and
volume may remain close to their upper ranges for a large part of the training
year (Wathen et al. 2000). Furthermore, elite athletes will tend to require a
greater degree of variation to optimise the effectiveness of their training (Plisk
and Stone 2003; Stone et al. 2000b).
In this section sample mesocycles will be described to illustrate the
periodisation strategies proposed for each phase of the training year for a
generic team sports athlete. The rationale behind the approaches used for each
of the respective training cycles is outlined below. Specific programme
variables, such as the length of each phase and exercise selection, will vary
according to the length of the playing season and demands of the particular
sport. A sample periodised plan is also presented in Tables 11.1 to 11.4.
Off-season
For the purposes of clarity, the ‘off-season’ phase for team sports will be
defined as the period prior to the start of structured technical and tactical
practices. Whether the strength and conditioning specialist actually has the
luxury of a supervised off-season period when the players report back after
the post-season break tends to depend on the willingness of the coaching staff
to delay the start of practices to allow them to do so. As a consequence of the
length of the playing season, particularly in European soccer and rugby
football leagues, this is often not the case.
Due to the long season of competition, it is vitally important to allow a
period of active rest following the end of the playing season (Wathen et al.
2000). That said, the length of the active rest period should be restricted to
avoid players entering off-season training in a detrained state. Similarly, in
view of the length of time players are engaged in supervised training it may
make sense to allow players to undertake the early initial part of off-season
training in an unsupervised setting. This will undoubtedly have a
psychological benefit in sports with an extended playing season by limiting
the monotony of the training ground environment.
Programming during the off-season will resemble the classical ‘general
preparation phase’. As such, training parameters during this time of year will
be characterised by relatively higher volume and frequency of training
conducted at lower intensity, and exercise selection will emphasise general
training modes for overall development. Accordingly, general strength
exercises that might be considered non-specific do still have merit during this
phase of the athlete’s preparation (Siff 2002). One aspect of this is that from
the point of view of training variation, lifts which are considered sportspecific should not be used exhaustively throughout the duration of the
training year (Wathen et al. 2000). The other determining factor is that the
training goals for this point in the training year should be building a
foundation of athleticism prior to concentrating on sport-specific development
in later phases.
As such, the starting point when prescribing off-season strength training
should be the results of the player’s musculoskeletal and movement screening
which should be undertaken when players report back to training at the
beginning of the new training year. Exercise selection can then address any
deficiencies identified and focus upon developing strength and motor abilities
for fundamental athletic movements, such as variations of the squat, lunge
and step up. Likewise, upper-body development during this phase will
emphasise generic pushing and pulling lifts and raises in various planes of
movement.
Pre-season
As alluded to previously, ‘pre-season’ for team sports will be deemed to be the
period of supervised training prior to the start of the playing season when
technical and tactical practices are concurrently scheduled. Accordingly,
during this phase physiological training must be planned in the context of the
other training and practices players are required to perform. From this point
of view, it is therefore vital that scheduling of training is carried out in
collaboration with the coaching staff.
Table 11.1 Representative off-season training mesocycle
The traditional linear format for training periodisation still merits
application during the pre-season phase of training for team sports.
Depending on the length of the pre-season in the particular sport, the initial
part of pre-season may be a continuation of the general preparation phase
begun during the off-season period. The remainder of the pre-season period
will resemble the ‘special preparation phase’ in the classic model. Broadly
there will be a progressive increase in training intensity prescribed and
correspondingly decreasing volume over the period. Training goals will show
a sequential shift from hypertrophy and/or strength-endurance to strength,
culminating in a power-oriented phase prior to the start of the playing season.
A suggested amendment to the classic linear model during the pre-season
preparation phase for team sports athletes is to shorten the duration of the
respective cycles (Hedrick 2002). The relative emphasis in terms of length and
nature of each mesocycle will be determined by the requirements of the sport
(Hedrick 2002). For example, in a sport that is reliant on lean body mass, the
higher volume hypertrophy-oriented cycles will be relatively longer and will
feature more prominently. Conversely, sports in which excessive hypertrophy
is counterproductive will favour strength and particularly power cycles.
Equally, the block periodisation approach (Issurin 2010) described in a
previous section may also be a viable alternative for the pre-season training
period. The pre-season may be divided into blocks of varying length,
depending on what is most appropriate given the time available. In
accordance with this approach, only two or three training goals will be
prioritised within each training block. The selection of training goals
emphasised in successive training blocks should be sequenced appropriately in
order to take advantage of the residual and cumulative effects of preceding
training cycles (Issurin 2010). For example, heavy resistance strength training
performed earlier in the pre-season period will have a favourable effect on
training outcomes when specialised power and speed development is
undertaken in later training cycles.
A further suggested manipulation is to incorporate day-to-day variation, by
varying prescribed RM loads during each respective training week. This
allows variation on multiple levels – both within and between microcycles.
Such an approach has been suggested to favour optimal training responses
(Stone et al. 2000b). As such the periodisation of training intensity and volume
during pre-season might comprise elements of both linear and undulating
periodisation, featuring weekly variation in intensity and volume within an
overall trend for progressively increasing intensity and decreasing volume
over the wider period.
Selection of strength training modes will similarly follow the sequential
progression in training goals during each respective phase from general
strength during the initial stages to power development and sport-specific
strength at the culmination of the pre-season training period (Wathen et al.
2000). Strength training exercise selection will thus feature progressive
introduction of speed-strength training modes and increasingly sport-specific
exercises as the player advances through pre-season training cycles.
Table 11.2 Representative pre-season training mesocycle
In-season
Undulating ‘non-linear’ periodisation models are typically suggested for inseason training (Wathen et al. 2000). The rationale is that this approach may
be better suited to maintain the athlete close to their peak throughout an
extended season of regular competitions. The variation in training
prescription within each training microcycle under this format will also allow
the strength and conditioning specialist to concurrently account for the
multiple training goals that are a common feature of team sports during the
playing season (Zatsiorsky and Kraemer 2006).
Alternative approaches to periodisation for the competition season are
however available. It has been highlighted that performing extended training
blocks characteristic of classical linear periodisation models in-season may not
be sufficient to maintain lean body mass in power sports athletes, such as
American football players (Allerheiligen 2003). Another approach advocated
for team sports players that are reliant on strength and power involves a
condensed linear periodisation format, featuring two-week training blocks
performed in series. It is suggested that this eight-week sequence can be
repeated throughout the length of the playing season (Allerheiligen 2003). A
similar ‘condensed linear’ approach involving weekly progression of training
parameters may also be employed in the same way (Prestes et al. 2009).
Another framework for in-season periodised training is the ‘summated
microcycles’ approach described in a previous section (Plisk and Stone 2003).
This approach may also be adapted in order to tailor respective microcycles to
the fixture list, by modifying the length of each summated cycle. Important
matches and games against particularly strong opponents represent natural
times to taper in-season training. Periods with many games concentrated into
a short space of time likewise require reduced training frequency. Both these
instances will necessitate an unloading week, in order to allow players to
enter these matches in peak condition. Hence, depending on the timing of
these games the summated microcycle may range from two to four weeks in
length, always concluding with an unloading week. Microcycles may
therefore feature a 1:1, 2:1 or 3:1 ratio of loading:unloading weeks. How these
variations of in-season microcycles are sequenced into the in-season plan will
depend on the fixture list and density of games in different periods within the
season.
It has been identified that average training intensity should be maintained
above 80 per cent 1-RM, in order to maintain strength levels during the course
of a playing season (Hoffman and Kang 2003). Similarly, two days per week
training frequency is often recommended for training during the competitive
phase (Wathen et al. 2000). High loads (at or above 80 per cent 1-RM, or at or
above 8–RM) are thus implemented two days per week for multi-joint lifts.
This loading scheme is shown to maintain, or even increase, strength levels
throughout the playing season in American football (Hoffman and Kang
2003).
In accordance with this, the majority of strength and conditioning coaches
in professional leagues typically report strength training twice per week inseason (Ebben and Blackard 2001; Ebben et al. 2004, 2005; Simenz et al. 2005).
However, these recommendations for in-season training need not be
excessively restrictive. A range of training frequencies and training
parameters are possible that will maintain average training frequency and
intensity within the ranges recommended. Players may train between one and
three times per week at various times in the season. Likewise, a variety of
intensity prescriptions may be used at different phases, while still maintaining
average training intensity above 80 per cent 1-RM throughout the season.
Conversely there will generally be opportunities during the season for more
intensive strength training – such as during fixtures in lesser competitions, or
mid-season breaks for international matches. In sports with an extended
competitive season, such as is seen in European soccer and rugby leagues, this
may be necessary to maintain physiological adaptations. This will tend to be
the case particularly in collision sports that are reliant upon high levels of lean
body mass, strength and power. At appropriate times mid-season, short
overload microcycles may therefore be implemented, followed by a taper
and/or active recovery. For these ‘shock blocks’ during the in-season period
the strength and conditioning specialist can therefore adopt an approach
similar to the block periodisation model (Issurin 2010).
Scheduling considerations for the weekly microcycle
During the period when players are not required to participate in competitive
matches, scheduling of weekly training during pre-season should aim to take
account of fitness and fatigue effects. As such, the sessions that require the
greatest neuromuscular co-ordination while the athletes are fresh will be
placed early in the week, whereas the more fatiguing workouts are performed
at the end of the week to allow the athlete the weekend to recover (Chiu and
Barnes 2003).
Table 11.3 Representative in-season training mesocycle
Table 11.4 Representative ‘peaking’ training mesocycle
Conversely, weekly scheduling of workouts in-season is dictated by the
dual need to allow the player to recover from the previous match and avoid
excessive residual fatigue at the end of the week in preparation for the next
game. This is true of all the variations of the in-season training cycles.
Similarly, the strength and conditioning specialist must be prepared on any
given day to revise the schedule and modify the session plan as is appropriate
to the current status of the player.
The sequencing of the training day appears key to minimising the degree to
which strength and power development are compromised by concurrent
metabolic conditioning work (Leveritt and Abernethy 1999). It has been
established that when strength (or speed-strength) training is prioritised in the
training day, and performed before conditioning, these interference effects can
be reduced (Leveritt and Abernethy 1999). Sequencing training in this way is
shown to optimise strength training responses of professional rugby league
players, to the extent that strength and power measures can be maintained
during the course of a lengthy (29-week) in-season period (Baker 2001).
Younger (college-aged) players can even increase strength and power scores
during the playing season by adopting this approach (Baker 2001).
Summary and conclusions
There are currently too few studies of sufficient length to make categorical
assertions regarding the superiority of one approach to periodisation over
another – particularly given the paucity of periodisation studies featuring
athlete subjects (Fleck 1999; Cissik et al. 2008). Furthermore, such debates may
be redundant – by definition periodisation concerns variation of training. As a
result it seems unlikely that a single periodised training scheme exists that
will elicit optimum results when applied for extended periods. Rather it seems
probable that a range of periodisation strategies implemented in combination
will produce the best results throughout players’ long-term training (Plisk and
Stone 2003).
Some evidence for this assertion was observed in the superior strength
gains during initial stages of training in strength-trained subjects with a daily
undulating periodised (DUP) model, in comparison to a linear periodisation
group (Rhea et al. 2002). This was attributed to the novelty of the DUP scheme
for the subjects, whose previous training had been characterised by linear
periodisation (Rhea et al. 2002). Equally the attenuated training response and
reports of training strain in the latter part of the study period in the DUP
group indicates that the continued use of this scheme in isolation may
similarly be unproductive (Rhea et al. 2002).
Hence, the best approach would appear to involve strategically combining
methods, implementing periodisation schemes in each training mesocycle
throughout the training year according to the needs of the respective phase of
players’ preparation (Plisk and Stone 2003). Periods in the off-season and preseason without competitive games will undoubtedly allow different
approaches to periodised training from those that will be conducive for
adequate recovery when matches are scheduled.
12
PHYSICAL PREPARATION FOR YOUTH SPORTS
Introduction
Youth training requires a specific and quite different approach to design and
implementation of physical preparation. As famously stated by Tudor Bompa,
young people cannot merely be considered ‘mini adults’ (Bompa 2000). The
physiological makeup of children and adolescents is markedly different from
that of mature adults (Naughton et al. 2000) – it follows that the parameters
applied to training design should reflect these differences.
The young athlete’s neural, hormonal and cardiovascular systems develop
with advances in biological age, leading to corresponding changes in
neuromuscular and athletic performance (Quatman et al. 2006). Rates of
development of a number of physiological and physical performance
parameters measured in young team sports athletes are shown to peak at
approximately the same time as they attain peak height velocity (Philippaerts
et al. 2006). The age at which this occurs is highly individual; ‘typical’ ages are
around 11.5 years for females (Barber-Westin et al. 2006) and for males in the
range of 13.8–14.2 years (Philippaerts et al. 2006). However, this does vary
considerably – levels of biological and physiological maturation can be
markedly different between young athletes of the same chronological age
(Bompa 2000; Kraemer and Fleck 2005).
What constitutes appropriate strength training and metabolic conditioning
for young team sports players is therefore determined by, and is specific to,
the individual player’s stage of physical development. The phase of growth
and maturation also influences the mechanism of training effects – such as
whether improvements are predominantly mediated by neural factors, or if
morphological and physiological adaptations play the greater role (Stratton et
al. 2004). The emotional and psychological maturity of the individual is
another important factor to be considered when designing and implementing
training for youth sports players (Kraemer and Fleck 2005; Stratton et al.
2004).
Another area of training for young athletes that has received less attention
is neuromuscular training, including specific instruction and practice of
fundamental movement mechanics. Neuromuscular and postural control as
well as movement biomechanics for jumping, landing, running and changing
direction can all be developed in the young team sports player as a means to
improve athleticism. Such development of fundamental movement skills may
also help reduce injury risk by equipping the young player to be better able to
react to challenges in the game environment.
Necessity of physical preparation for young team sports
players
Major public health concerns are the sedentary behaviours and declining
levels of physical activity of youth worldwide (Hills et al. 2007). As a result of
modern sedentary lifestyles, young people are also often not physically
prepared for the rigours of youth sports (Faigenbaum and Schram 2004;
Kraemer and Fleck 2005). Accordingly, the increase in participation in
organised youth sports in North America has been accompanied by a dramatic
rise in sport-related injuries (Goldberg et al. 2007; Kraemer and Fleck 2005). It
has not been documented whether this increase in the number of injuries has
been proportional to the increased numbers participating, or whether there
has been a relative increase in the rate of injury among these young players.
Whatever the case, approximately one-third of young athletes participating
in organised sports in the United States sustain injuries requiring medical
attention (Barber-Westin et al. 2005). Incidence of medical treatment for sports
injuries peaks between the ages of 5 and 14 years and then progressively
declines thereafter (Adirim and Cheng 2003). The ankle and knee are the most
frequent sites of injury reported in these young athletes (Adirim and Cheng
2003; Barber-Westin et al. 2005). Youth sports players also appear to be at
greater risk of low back pain and acute lumbar spine injury, particularly
during adolescence (Kujala et al. 1996).
Inadequate physical preparation is believed to play a role in the majority of
sport-related injuries in young athletes (Kraemer and Fleck 2005). Conditions
of muscle fatigue do place athletes at greater risk of injury: tired players in the
latter stages of a game are more likely to sustain injury than when they are
fresh. Likewise, players are more likely to be injured early in the season when
their fitness levels are not up to standard (Thacker et al. 2003). Injuries
incurred during youth sports are a commonly cited reason for ceasing to
participate in sport as an adult (Mackay et al. 2004). This has negative health
implications given the established links between physical inactivity, obesity
and chronic disease in adulthood (Hills et al. 2007). From this perspective,
prevention of injury in youth sports assumes increased importance, beyond
merely enhancing young players’ sports performance (Mackay et al. 2004).
Physical preparation, which includes strength training in addition to
training to develop cardiorespiratory fitness, is therefore an established and
integral part of strategies employed to prevent sports injuries, including those
in children and youth sports (Mackay et al. 2004). Inadequate motor skills are
another factor identified as increasing youth sports injury risk (Adirim and
Cheng 2003). Again, these abilities may be developed via appropriate athletic
preparation.
Addressing fundamental movement skill development
Pre-adolescents exhibit considerable potential for motor learning. Many
authors state that complex motor skills are not mastered until ages 10–12
(Adirim and Cheng 2003; Barber-Westin et al. 2006). It is suggested that there
is a prime window of opportunity for motor development prior to puberty.
Teaching basic movement mechanics for running, decelerating and changing
direction should form a fundamental part of training for all young players.
Performing complex whole-body training exercises is advocated to enhance
co-ordination and athleticism. Such training also develops kinaesthetic
awareness and proprioception, making the young player better able to retain
their balance under pressure from opponents and adjust to uneven terrain.
Improving these functional abilities might therefore have a protective effect,
helping to guard against injury (Faigenbaum and Schram 2004).
It has been identified that prepubescent athletes have a tendency to exhibit
neuromuscular control deficits relating to aberrant lower alignment during
various tasks (Barber-Westin et al. 2005). This is indicative of impaired ability
to control lower limb joint motion, and as such is associated with increased
injury risk (Ford et al. 2003). Training to specifically improve lower limb
neuromuscular control would therefore appear important in order to correct
the potentially injurious lower limb alignment when it is observed in these
prepubescent team sports players. Young females in particular show these
traits throughout their development (Barber-Westin et al. 2005). Recent
studies show that post-pubescent male athletes may also continue to exhibit
valgus lower limb alignment during drop landing tasks, despite markedly
increased lower limb strength levels (Barber-Westin et al. 2006; Noyes et al.
2005). It follows that appropriate screening and neuromuscular training should
not be neglected with adolescent male team sports players.
In prepubescent players such neuromuscular control issues and injurious
lower limb alignment are offset by their lower body mass and movement
velocity (Barber-Westin et al. 2006). In contrast, adolescent players are much
heavier and generate greater forces and movement speeds – markedly
increasing imposed stresses as a result of their greater inertia and momentum
(Barber-Westin et al. 2006). The consequences of any deficits in
neuromuscular control in adolescent players are therefore greatly magnified.
Supporting growth, development and body composition
Regular physical activity in combination with proper nutrition exerts a major
influence upon growth and development in children and adolescents. It is
suggested that there is a threshold level of physical activity which, in
combination with proper nutrition, is required in order that young players
achieve their genetic potential in terms of growth and maturation (Hills et al.
2007). A structured programme of physical preparation offers a means to
ensure that this is achieved, particularly at critical periods in the young
player’s growth and maturation.
From this perspective, appropriate physical preparation assumes increased
importance to a young player’s athletic development given the apparent lack
of habitual physical activity elsewhere in their lifestyle. The absence of such a
programme of physical preparation to help achieve a threshold level of
physical activity may otherwise hinder young players’ development during
critical periods in their growth and maturation to the extent that they may not
fulfil their genetic potential (Hills et al. 2007).
Furthermore, dedicated training for youth sports also appears vital to help
these players maintain lean body composition in view of the declining
physical activity and rising obesity among youth in general. This would
appear to be particularly important during certain critical periods of growth
and maturation. For example, during and following puberty females exhibit
characteristic changes in body composition including gains in body fat mass,
which can be unfavourable to performance and potentially to health
(Naughton et al. 2000). Appropriate resistance training, in conjunction with
aerobic exercise, has been proposed for losing body fat and for weight
maintenance with young people – in much the same way as is recommended
for adults (Faigenbaum and Schram 2004). In view of the increasing incidence
of childhood obesity the potential of physical preparation which includes
resistance training to favourably alter body composition is also advantageous
from a health perspective (Hills et al. 2007).
Conversely, the potential for strength training to increase lean body mass is
of relevance to players in collision sports from a selection and performance
perspective. In sports such as rugby and American football, physical size is a
determining factor for participation at higher levels (Olds 2001). Young
players are naturally predisposed to – and selected for – particular playing
positions on the basis of their anthropometric (height and body mass)
characteristics as well as their strength capabilities (Duthie et al. 2003).
Without a background of systematic strength training, young players are
unlikely to have undergone the requisite physical development for selection at
the highest levels.
Influence of growth and maturation on the
development of physical performance capabilities
The scope for improvements in different aspects of fitness and motor
performance varies as the young athlete passes through different stages of
physical maturation. Rates of development of a number of physiological
parameters appear to peak at around the same time as peak height velocity
(stage of maximal growth in height) in young team sports players
(Philippaerts et al. 2006). The age that peak height velocity is attained varies
considerably, but is reported to occur at around 11.5 years for females (BarberWestin et al. 2006) and for males in the range of 13.8–14.2 years (Philippaerts
et al. 2006).
During puberty spontaneous growth-related improvements in motor
performance and physiological parameters occur. A longitudinal study of
youth soccer players showed that these natural gains may plateau during the
interval prior to the young athlete reaching peak height velocity –
performance may even decline during this period, as occurs with 30m speed
scores (Philippaerts et al. 2006). Once the player then reaches the age when
peak height velocity is attained, several of these natural gains in physiological
and motor performance scores appear to reach their peak rate of development.
In the 12–18 months following peak height velocity, declining rates of growthrelated improvements are observed in several parameters (Philippaerts et al.
2006). Hence, scores in motor performance (in the absence of training
interventions) appear to plateau at the end of this phase of development in
youth sports players.
Prepubescent athletes exhibit lower levels of mechanical efficiency
compared to adolescents. Although this improves as the young athlete
progresses through puberty, adolescent athletes still demonstrate lower
mechanical efficiency than adults (Naughton et al. 2000). It follows that there
is considerable scope for this aspect of performance to be improved via
specific instruction and practice. Exercise economy has been identified as an
area for development in young athletes (Naughton et al. 2000) – allowing the
young player to sustain a higher relative work rate throughout the course of a
match.
As males pass through puberty they undergo a ‘neuromuscular spurt’.
Accompanied by limb growth and favourable changes in body composition
(increased muscle mass relative to fat mass), these natural gains in strength
and neuromuscular performance bring about a natural improvement in male
players’ biomechanics during movement (Quatman et al. 2006). One observed
aspect of this improvement is an enhanced ability to dissipate ground reaction
forces upon landing. These landing impact forces in turn directly influence the
loading absorbed through lower limb joints (Hewett et al. 1999).
This ‘neuromuscular spurt’ phenomenon does not occur in females. The
lack of any marked improvement in neuromuscular power and control, in
combination with limb growth and body mass gains, in fact results in reduced
lower limb stability in adolescent females (Quatman et al. 2006). Specifically,
rapid growth of in particular the lower limbs during puberty increases the
lengths of levers of the lower limb, and this is compounded by concurrent
increases in body mass, so that female players face greater difficulty
controlling motion of the trunk and lower limbs during athletic tasks; this has
consequences for loads placed on the knee joint (Myer et al. 2008). Female
players characteristically exhibit a tendency for potentially injurious lower
limb alignment and movement mechanics as adolescents (Barber-Westin et al.
2006; Quatman et al. 2006). In the absence of neuromuscular training, female
players also often preferentially recruit the quadriceps over the hamstring
muscles during activity: a phenomenon known as ‘quadriceps dominance’
(Ford et al. 2003). Such biomechanical factors and aberrant recruitment
patterns are implicated in the gender differences in rates of ACL injury postpuberty, which is not seen before this stage of development. Various studies
report adolescent female players suffer 2–10 times greater incidence of ACL
injury compared to male players, depending on the sport (Goldberg et al.
2007).
Changes in both musculoskeletal and cardiorespiratory systems during and
following puberty have major implications for metabolic conditioning
(Naughton et al. 2000). There are marked differences between prepubescent
and adolescent players in terms of their responses to anaerobic and aerobic
exercise (McManus and Armstrong 2008). Both children and adolescents
exhibit gains in cardiorespiratory fitness with aerobic training (Naughton et
al. 2000). Significant gains can be made particularly during puberty in young
players as they reach peak height velocity (around 14 years of age in boys, 12
years in girls), partly due to aforementioned maturation effects (Philippaerts et
al. 2006). Overall gains in aerobic fitness (for example, VO2peak) reported in
response to metabolic conditioning with young athletes are, however,
suggested to be less than those observed with adults (Matos and Winsely
2007).
Prior to puberty the glycolytic metabolic system is less well developed and
this is reflected in young athletes’ metabolic responses to exercise, with
oxidative metabolism dominating (Boisseau and Delamarche 2000). This may
in part reflect differences in muscle fibre profiles pre- and post-puberty.
Prepubescent athletes are reported to have a greater proportion of type I fibres
compared to untrained adults; whereas this is not evident in adolescent
athletes (Boisseau and Delamarche 2000). During puberty the capacity of
young players for anaerobic (glycolytic) metabolism progressively increases
(Naughton et al. 2000). The rate of maturation-related improvements in
anaerobic enzyme content and activity during puberty appears to peak around
the time the young athlete’s growth curve attains peak height velocity
(Philippaerts et al. 2006).
‘Overuse’ injury incidence in youth sports
When organising participation of adolescents in physical training and
organised sports, it is important to recognise that young people are still
growing (Bompa 2000; Kraemer and Fleck 2005). Coaches must consider the
fact that the bones, muscles and connective tissues of the young athlete are
not yet fully developed. As such, high volumes of repetitive practice may
render the young player susceptible to overuse injury. This dictates that there
is a need not only for age-appropriate practice and competition schedules but
also for young players’ physical preparation to be designed to reflect their
specific stage of growth and maturation.
Biomechanical factors seem to play a role in the incidence of overuse
injuries with youth sports participation. The rapid changes in the size and
length of limbs during growth spurts alter the mechanics of athletic
movements (Hawkins and Metheny 2001). As young players grow, this
actually increases the forces and mechanical stresses involved in sports
movements. When the young player is undergoing a growth spurt particular
care should be taken, in view of the combined strain associated with rapid
growth and physical stresses during competition and practices (Naughton et
al. 2000). During this time, the immature skeleton may be more susceptible to
injury than at later stages in the player’s development – lumbar spine injuries
particularly appear to increase in young adolescent athletes (Kujala et al.
1996). Growing cartilage is similarly more prone to injury in comparison to
when the player reaches physical maturity, which can also be a factor in some
overuse injuries (Adirim and Cheng 2003).
Given time, muscles and connective tissues respond to accommodate these
growth-related changes; however, there is a time lag before this adaptation
takes place (Hawkins and Metheny 2001). Under normal circumstances
connective tissues remain within their failure limits during this lag phase.
However, during puberty in males particularly there is a rapid increase in
body mass and strength. As tendon and ligament strength respond relatively
more slowly than muscle, these structures are placed closer to their failure
limits in young players during and immediately following periods of rapid
growth (Hawkins and Metheny 2001). Repeatedly performing a given sports
movement during this sensitive phase in the young player’s development can
lead to overuse injury.
The point of attachment of tendon to bone (the apophysis) is an area
particularly prone to overuse injury in the growing player (Adirim and Cheng
2003). Microtrauma injury – apophysitis – commonly occurs at the heel
(Sever’s disease) and the elbow (‘Little League elbow’) in younger children
(ages 7–10). A similar condition – ‘Osgood–Schlatter disease’ – occurs at the
insertion of the patella tendon and is often seen in young people aged 11–15
years (Adirim and Cheng 2003).
In certain youth sports, there is a risk of overuse injuries simply due to the
strains involved in repetitive performance of a particular sports skill
movement during practices and games – such as in throwing sports. In the
United States it has been estimated that these overuse injuries make up
approximately one-half of all sport-related injuries requiring medical
treatment (Hawkins and Metheny 2001). In an effort to combat this, some
governing bodies suggest limits for the number of repetitions of particular
sports movements (such as the number of throws) that should be performed
by the young player during a practice session (Hawkins and Metheny 2001).
A long-term perspective on youth training
It is critical when training young athletes to remain mindful of the processes
of growth and maturation and how these will interact with the training stress
placed upon the young athlete. Relative age and stage of growth and
maturation are key factors when designing an appropriate training plan for
young team sports players; this may vary widely between players competing
at the same age group. Young athletes are often stratified into ‘early
developers’ and ‘late developers’ in terms of the relative chronological age at
which biological, physiological and neuromuscular performance changes
occur. Two young players at the same ‘chronological’ age can therefore differ
considerably in terms of their relative stage of biological and physiological
maturation (Bompa 2000; Kraemer and Fleck 2005).
These considerations would clearly seem to necessitate a different approach
in terms of training prescription for young and developing athletes, in relation
to what is optimal for an adult. Training guidelines for young players should
also take account of individual players’ respective stage of growth and
maturation (Gamble 2008). Unfortunately, the financial incentives for those
who achieve success in sport, such as scholarships and professional contracts,
often lead to excessive and inappropriate demands being placed on the young
player, particularly those who have been identified as ‘talented’ or elite
performers at age-grade level (Malina 2009). The growing awareness of ‘sportspecific training methods’ among coaches, parents and the young players
themselves may similarly result in pressure to solely prescribe and perform
training that mimics the chosen sport in which the young player participates.
The dangers of early specialisation
Authorities on the topic of long-term athlete development stress the need for
variety in terms of not only training activities but also sports participation
(Bompa 2000). Participating in multiple sports and athletic activities will
provide young athletes with opportunities to develop a greater range of motor
and cognitive skills that will ultimately benefit their performance in the sport
in which they eventually choose to specialise (Malina 2009). It therefore
appears that participating in multiple sports during the athlete’s
developmental years may in fact ultimately confer an advantage in
performance terms relative to those who fall into early specialisation (Malina
2010).
Unfortunately, despite the benefits ascribed to varied sports participation,
those who have been selected into elite or national-level programmes will in
fact often participate much less in other sports (Malina 2010). One reason for
this is that the practice and competition schedule no longer permits the athlete
the time to do so. In many sports, for example soccer, those young athletes
who show promise will typically be selected for representative teams in
addition to their existing club and school team, so that they will often
compete several times in a week.
Another reason that talented young athletes cease to participate in other
sports is because to do so is in many cases actively discouraged by the coach
in their primary sport (Malina 2009). Reports in the skill acquisition literature
regarding the potential benefits of deliberate practice at an early age with
respect to the long-term development of expert performance (Ericsson 2007) to
some extent promote this early sport specialisation. Similarly, the 10-year or
10,000-hour rule in relation to experience and deliberate practice with respect
to attaining mastery in a given discipline may encourage parents and coaches
to attempt to get an ‘early start’ in the chosen sport with their child athlete
(Malina 2010). Many professional sports teams and national governing bodies
likewise increasingly begin their recruitment of junior athletes at a very
young age.
As discussed in a previous section, the cumulative strains of high volumes
of repetitious sports practice are identified as a major cause of overuse injury
among young athletes (Valovich McLeod et al. 2011). This poses particular risk
at sensitive phases in the athlete’s growth and development (Hawkins and
Metheny 2001). Early specialisation is a related causal factor in the scenario of
excessive participation in practice and competition, which likewise
predisposes young athletes to overuse injury (Malina 2010).
In addition to the physical strains of early sports specialisation, there are
also psychological and psychosocial ill effects that must be considered (Malina
2009). This is likely a factor in the high rates of burnout observed in sports
that promote early specialisation – for example, women’s tennis. It is
therefore advocated that the young player should only specialise in terms of
sport and playing position as they advance into late adolescence – and much
the same applies in terms of physical preparation.
A pyramid model for athletic development can be applied to youth training.
Logically, training to build young athletes should begin at the foundation and
build upwards. It follows that in developing ‘structural integrity’, mobility
and stability should be the first priority when training young players. In turn
these qualities underpin the player’s ability to perform fundamental
movements that are common to all sports. The young athletes’ fundamental
movement abilities will determine their ability to perform sport-specific
movements. As such there is little point in trying to impose sport-specific
strength or neuromuscular training upon deficient fundamental movement
capabilities. It follows that training activities at this stage of the athlete’s
physical preparation should predominantly feature fundamental athletic
movements alongside appropriate movement skills instruction and training
(Myer et al. 2006a). Employing a greater variety of conditioning modes is
advocated for young athletes, for example there should be greater emphasis
on cross training modes, in contrast to what is undertaken with mature
athletes (Bompa 2000; Gamble 2008).
Strength training for young team sports players
Safety and effectiveness of youth resistance training
The benefits of youth resistance training are well documented and are
becoming universally accepted among health professionals, particularly in the
US (Faigenbaum et al. 2009; Faigenbaum and Schram 2004) but also
increasingly in the UK (Stratton et al. 2004). Fitness professional associations
and health organisations are now in agreement that age-appropriate youth
resistance training is safe and beneficial when performed under qualified
supervision (Faigenbaum and Schram 2004; Kraemer and Fleck 2005; Stratton
et al. 2004). However, public recognition of these benefits continues to lag
behind, and misunderstanding and misconceptions remain.
Historically the concerns about youth resistance training stem from a
perceived risk of damaging growth plates, which could potentially interfere
with normal growth. In fact, such damage to growth plates has never been
documented with strength training programmes for children that were
administered and supervised by qualified personnel. Studies employing
appropriate youth resistance training in fact report very low incidence of
injuries of any type (Faigenbaum et al. 2009). Far from stunting growth, the
contemporary evidence is that resistance training, in combination with proper
nutrition, has the potential to enhance growth within genetic bounds at all
stages of development (Faigenbaum et al. 2009).
The most frequent causes of injury when children and adolescents
undertake resistance training are incorrect lifting technique, attempting to lift
excessive loads, inappropriate use of equipment, and absence of qualified
supervision (Faigenbaum et al. 2009). All of these factors can be reduced or
eliminated with properly administered and supervised training (Stratton et al.
2004). Naturally, young players, as with any inexperienced lifters, should only
engage in strength training programmes prepared by qualified coaches, with
safe equipment, and supervised by qualified instructors. However, if these
conditions are met, there are no safety grounds to preclude young players
undertaking supervised strength training (Kraemer and Fleck 2005).
The reality is that children are exposed to far greater forces – and of longer
duration – during sports and recreational physical activity than those
encountered during strength training, even if they were to perform a maximal
lift (Faigenbaum et al. 2009). Of all resistance training exercises, the Olympic
lifts possibly impose the greatest forces upon the young musculoskeletal
system. Even so, injury data suggest that Olympic weightlifting training and
competition conducted under the supervision of qualified coaching is one of
the safer athletic activities engaged in by young athletes (Hamill 1994).
Mechanisms for strength gains in prepubescent and
adolescent athletes
Previously, the presumption had been that strength training prior to puberty
was not viable or effective. However, it now appears that prepubescents
exhibit significant scope for strength gains, far beyond those attributable to
normal growth and maturation (Faigenbaum et al. 2009). Relative gains in
strength documented with resistance training in prepubescent subjects are in
fact of similar magnitude to those shown by adolescents (Faigenbaum et al.
2009).
That said, there are trends for greater absolute strength gains in adolescent
subjects. Puberty triggers major physiological and hormonal changes
(Naughton et al. 2000). Increases in circulating anabolic hormones during
puberty impact considerably on how the young player responds to strength
training. Lower levels of circulating anabolic hormones limit the contribution
of hypertrophy (lean tissue growth) to strength gains (Faigenbaum et al. 2009).
The changes to muscles that do occur appear to be more qualitative than
quantitative. Neural effects thus appear to underpin many of the gains from
resistance training in these younger participants.
Such neural adaptations are suggested to include improved recruitment and
activation of the muscles mobilised during the training movement. Enhanced
motor co-ordination, both within and between muscle groups, is also thought
to contribute to strength gains following training. By the nature of these
training adaptations, such strength gains would seem to be less permanent;
prepubescent players will exhibit marked detraining effects once regular
resistance training is discontinued (Faigenbaum et al. 2009). However, modest
maintenance programmes (one or two days per week) do appear to be
sufficient to sustain strength gains.
The greater hormonal response to resistance training in adolescents than at
earlier stages of development leads to structural changes to the muscles and
associated connective tissues (Faigenbaum et al. 2009). As a result, marked
changes in terms of muscle hypertrophy and gains in fat-free mass are seen in
this older age group. Such increases in muscle cross-sectional area and
changes in muscle proteins therefore augment the gains in strength of neural
origin that occur. This is the case especially among adolescent male players.
However, the power per kilogram (body mass) that adolescents are capable of
generating is still less than the corresponding values for adults (Naughton et
al. 2000).
Strength training for performance enhancement in
youth Sports
It is becoming recognised that young players can experience similar benefits
from strength training to those observed with adults (Faigenbaum et al. 2009).
All youth sports demand strength and power to varying degrees, in order to
overcome the player’s own body weight when moving and the resistance of
opponents – particularly in contact sports. It follows that developing strength
via resistance training should positively impact upon performance in the
young player’s sport (Stratton et al. 2004).
The effects of strength training in young players, which include increased
strength and improved motor skills and co-ordination, have the potential to
improve athleticism. Improvements in scores on motor performance measures
are often observed following resistance training in children (Stratton et al.
2004). Positive changes have been noted in vertical jump, standing long jump,
sprint times and agility run times (Faigenbaum et al. 2009).
The available data from the limited number of studies that have been
published indicate that increases in flexibility can be made, particularly if the
resistance training incorporates specific stretching, warm-up and cool-down
(Stratton et al. 2004). This appears to refute concerns in some youth sports that
resistance training will lead to the young athlete becoming muscle-bound and
consequently decrease their flexibility and range of motion. Warm-up prior to
training and team practices should comprise dynamic flexibility exercises; this
form of stretching appears to offer most effective preparation for dynamic
activity (Little and Williams 2006a).
Strength training for injury prevention
Participation in team sports does involve some inherent risk of injury.
Although these injuries can never be entirely eliminated, appropriate training
can help to reduce the number of injuries and severity of injuries that do
occur. Young players are subject to additional risk due to physiological and
developmental factors. The strains on connective tissues during growth and
the changing properties of the growing tissues render these structures more
prone to injury in the young player than is the case with adults (Adirim and
Cheng 2003). Strengthening muscles and connective tissues via strength
training offers a means to increase the forces they are capable of sustaining,
helping to make the young player more resistant to soft tissue injury. In
adolescents particularly, it is important to strengthen these connective tissues
to accommodate the rapid gains in strength and body mass that occur during
puberty (Adirim and Cheng 2003).
Strengthening muscles around upper-limb and lower-limb joints via
appropriate training similarly offers a means to increase the active stability
provided to these joints, which can serve a protective function (Stratton et al.
2004). Strength training was shown to improve neuromuscular control indices
during jumping and landing in female adolescent athletes (Lephart et al. 2005).
Such development of motor control and co-ordination helps to improve
postural balance, dynamic stabilisation and active joint stability – all of which
are beneficial in reducing incidence of lower limb injury.
In the case of young female players, lower limb strength development in
general and hamstring strengthening in particular should be a major area of
emphasis (Barber-Westin et al. 2006). Measures of hamstring strength are
reported to plateau very early in female athletes’ physical development – with
older age groups (13–17 years) showing no significant gains on this measure
compared to 11-year-old females (Barber-Westin et al. 2006). The hamstrings
compress the knee joint and oppose anterior shear forces during weightbearing closed-chain movements – as a result of these functions the hamstring
is described as an ‘ACL agonist’ (Hewett et al. 1999). The relative weakness of
the hamstrings of female players is of clinical relevance given the two to ten
times greater rates of non-contact knee ligament injury in adolescent female
athletes, compared with males (Goldberg et al. 2007).
Prepubescent athletes are shown to have a greater tendency than older
populations to exhibit asymmetrical lower limb performance, based on scores
with single-leg hopping functional tests (Barber-Westin et al. 2005). In the
absence of intervention such imbalances may persist post-puberty in both
males and females (Barber-Westin et al. 2006). Appropriate strength training
offers a means to help correct such right–left imbalances in lower limb
function, particularly in combination with plyometric or dynamic balance
training (Myer et al. 2006a). This role of strength training in correcting sideto-side strength imbalances is crucial for young players at all stages of
development. Strength and flexibility imbalances are identified as major risk
factors for injury (Knapik et al. 1991). Strength imbalances can have negative
consequences for both limbs: over-reliance may place excessive strain on the
stronger limb; whereas the weaker limb is less able to actively counter
injurious forces (Ford et al. 2003).
Studies show that young players who have strength training experience
tend to sustain fewer injuries (Faigenbaum and Schram 2004). Incidence of
injury in strength-trained youngsters is approximately one-third that of young
athletes without any strength training experience (Bompa 2000). As well as
serving to reduce overall incidence of injury, strength training can also help to
reduce the severity of injuries. Following injury, strength-trained young
players also respond better to rehabilitation (Faigenbaum and Schram 2004).
Hence strength training can assist the young player in making a more rapid
return to training and competition (Kraemer and Fleck 2005).
For these reasons, strength training is recommended in a ‘preconditioning’
role for young people before they start to compete in organised youth sports
(Bompa 2000). Young players who are better conditioned and less prone to
injury due to appropriate physical preparation – including strength training –
are more likely to continue to participate in youth sports. In this way strength
training can help reduce drop-out rates, which in turn can help keep
youngsters healthy in later life (Faigenbaum and Schram 2004).
Aside from the benefits of general strength training, targeted strength
training involving particular exercises may also be used to guard against
certain injuries that commonly occur in sports. This targeted injury
prevention role for strength training is often overlooked, particularly in young
athletes. Too often exercises to strengthen areas that are prone to injury are
only prescribed once an injury has already occurred. Unfortunately, there are
currently an insufficient number of prospective studies in the literature
involving youth sports players to provide evidence-based training guidelines
regarding effective training for injury prevention (Mackay et al. 2004).
Training to develop bone health and connective tissue
In much the same way as for adults, it is established that physical activity has
positive links to bone mineral density and connective tissue integrity in young
people (Greene and Naughton 2006; Stratton et al. 2004). Although genetics is
a determining factor, the major stimulus for accumulation of bone mass and
mineral content is mechanical loading (Greene and Naughton 2006). The
cross-sectional area and architecture of connective tissues are also trainable;
appropriate strength training can therefore also be applied to develop strength
and size of tendons and ligaments (Conroy and Earle 2000).
Mechanical loads must exceed a threshold in order to trigger adaptive
responses (Conroy and Earle 2000). In accordance with this, both high-force
weight-bearing and strength-type activities appear most suitable to elicit bone
and connective tissue adaptations. Dynamic skeletal loading – that is, loading
during movement – appears to be relatively more osteogenic than the same
loads applied under static conditions (Greene and Naughton 2006). It follows
that relatively high mechanical loading occurring during dynamic training
activities should result in the greatest bone adaptation.
Recommended exercises generally involve weight bearing – so that the
young player’s own body weight provides additional loading (Conroy and
Earle 2000). Athletic activities that involve high ground reaction forces are
associated with increased bone mineral content and density (Greene and
Naughton 2006). Sprinting, jumping and other lower-body plyometric
exercises are identified as good training activities for developing bone
strength as they offer high ground reaction forces and impact loading. Young
athletes in all running-based sports and athletic events can benefit from these
training modes. However, the volume of such training (for example, total foot
contacts for plyometric training) must be monitored in order to avoid
excessive strains and potential overuse injury.
Applying resistance via strength training is another means to generate the
mechanical stresses required for an osteogenic response (Greene and
Naughton 2006). This particular role of strength training for young athletes
has been termed ‘anatomical adaptation’ (Bompa 2000). Associated positive
effects include increased strength of supporting connective tissues and passive
joint stability, as well as increased bone density and tensile strength
(Faigenbaum and Schram 2004). In the same way as weight-bearing activities
are recommended, ‘structural’ multi-joint strength training lifts (for example,
variations of the squat, lunge and step up) offer a means to elicit whole-body
skeletal adaptations. The strength and conditioning specialist can also harness
site-specific gains in strength and cross-sectional area of bone and connective
tissues associated with the muscles recruited during particular strength
training exercises (Conroy and Earle 2000). Specifically, strength training
exercises can be used to strengthen bones and connective tissues at particular
sites that tend to be exposed to strain in the particular sport – such as the
shoulder girdle in contact sports.
Immediately prior to and during puberty appears to be a key phase that
offers a window of opportunity for skeletal adaptations (Greene and
Naughton 2006). It is suggested that osteogenic training activities can
therefore be used to amplify the skeletal growth and growth-related gains in
lean body mass that occur naturally during these stages. Studies have shown
that post-puberty females may be less responsive to skeletal adaptation – this
suggests that there is an earlier and narrower window of opportunity for
developing bone and associated connective tissues with female players
(Greene and Naughton 2006).
Increases in bone density brought about by strength training are of
relevance to female players from a longer-term health perspective. Females
have a higher incidence of osteoporosis in comparison to males during late
adulthood. During adolescence the growing skeleton seems to be particularly
responsive to training (Greene and Naughton 2006). For this reason, young
players (females in particular) are recommended to perform dynamic weightbearing exercise and appropriate strength training during childhood and
adolescence (Conroy and Earle 2000; Kraemer and Fleck 2005). Increasing the
female player’s bone mineral content at this stage of development is likely to
have a favourable impact on their risk profile for osteoporosis in later life.
Metabolic conditioning
Responsiveness of young athletes to different forms of
metabolic conditioning
Data from early studies in the literature suggested that prior to puberty young
athletes might be less responsive to aerobic training. More recent studies have
not found this to be the case, so some authors suggest that the equivocal
findings were merely a result of the training provided being insufficiently
taxing to elicit a significant response (McManus and Armstrong 2008). It now
appears that a variety of endurance training modes and protocols produce
gains in aerobic capacity with prepubescent subjects (Baquet et al. 2002, 2010;
McManus et al. 2005).
As discussed in a previous section, prepubescent athletes exhibit a lower
capacity for glycolytic metabolism. In view of this, it had previously been
suggested that prepubescents are not amenable to performing anaerobic forms
of training, such as interval conditioning. Guidelines in the literature have
therefore advocated that these forms of metabolic conditioning should be
avoided at this stage of development. However, over recent years a growing
body of data have accumulated that challenge this assertion (McManus and
Armstrong 2008). These studies find that while the nature of the metabolic
responses of prepubescent athletes to high-intensity interval training may
differ, they remain highly capable of performing this form of exercise and
demonstrate a propensity to adapt very positively to high-intensity interval
training (McManus and Armstrong 2008).
Mechanisms of training adaptations
There is a lack of data from young athletes, in part due to ethical reasons,
which preclude invasive methods of assessment being undertaken with
children. In particular, it is not yet clear to what extent central
cardiorespiratory adaptations or peripheral adaptations are responsible for the
improvements in endurance seen in prepubescent, pubertal and adolescent
athletes in response to different training interventions (Baquet et al. 2010). It
has been speculated by Baquet and colleagues (2010) that the relative
contribution of central versus peripheral adaptations might differ according to
the mode, format and intensity of conditioning employed.
It is also likely that different mechanisms may be attributed to the training
responses observed following high-intensity anaerobic conditioning with
prepubescent versus adolescent athletes. For example, the limited capacity of
prepubescent athletes for glycolytic metabolism results in reduced levels of
lactate production during this form of exercise. Lower muscle lactate
concentrations are reported with prepubescent athletes, and the drop in
muscle pH is correspondingly less due to the reduced levels of H+ ions
released with lactate production via glycolysis (Boisseau and Delamarche
2000). It follows that this is likely to limit specific training adaptations
associated with buffering H+ ions and clearing lactate that are seen following
puberty in response to anaerobic training.
Aerobic conditioning
The training parameters for metabolic conditioning may vary according to the
respective stages of growth and maturation, particularly in terms of overall
volume and duration. Prior to puberty it is likewise suggested that the rate of
progression in terms of duration or distances covered should be gradual and
relatively conservative for younger athletes (Bompa 2000). Both these
perspectives point to a less regimented approach than that used with older
groups of players. In this way conditioning not only remains enjoyable but
also the young player can self-regulate work intensity.
The selection of training modes employed should also alter as the player
grows and matures. A wider variety of activities and cross training modes is
advocated for prepubescent players (Bompa 2000; Kraemer and Fleck 2005). It
is recommended that endurance training activities employed with
prepubescent players should be selected to avoid monotony and aim to
incorporate a fun element (Bompa 2000; Kraemer and Fleck 2005). As the
young player matures, training guidelines change to reflect corresponding
changes in physical capabilities: training modes will become more specific to
the sport and the intensity of conditioning activities may likewise increase.
Running-based interval conditioning has been used successfully to improve
the aerobic capacities of young team sports players (Buchheit et al. 2009).
Skill- and sport-related movement drills can also be adapted for conditioning
purposes (Bompa 2000; Hoff 2005). Ball games with simplified rules are
another good choice for conditioning activities with these young players
(Buchheit et al. 2009). As the young player moves into adolescence, there will
be an increasing demand for the training modes used for metabolic
conditioning to become more specific to the sport.
Anaerobic conditioning modes
During puberty young athletes’ capacity for anaerobic metabolism increases
(Philippaerts et al. 2006). However, each individual player’s tolerance for
training will differ according to their stage of development. This can vary
widely in a group of players of the same chronological age (Bompa 2000;
Kraemer and Fleck 2005). This must be considered particularly when training
players of an age where they may be undergoing puberty.
Adolescence is identified as the time for specialisation in young players’
physical preparation (Bompa 2000; Naughton et al. 2000). Physiological
changes during puberty increase young players’ capacity for, and
responsiveness to, anaerobic training (Naughton et al. 2000). This form of
conditioning is a requirement of the majority of team sports; it therefore
follows that anaerobic training should feature increasingly in adolescent
players’ physical preparation.
Various modes of interval training are shown to be effective in improving
measures of endurance fitness and performance indices with team sports
players (Helgerud et al. 2001; Hoff et al. 2002). High-intensity interval hill
running was shown to elicit significant improvements, including lactate
threshold, in young soccer players, which importantly also carried over to
measures of soccer performance during matches (Helgerud et al. 2001). A
soccer-specific protocol running through a set course involving dribbling a
ball alternated with backwards and forwards shuttle sprints through cones is
also reported to elicit sufficiently high intensities (93 per cent HRmax or 91
per cent VO2max) for developing anaerobic capacity (Hoff et al. 2002).
Summary
The need for different aspects of physical preparation – including strength
training, metabolic conditioning and also neuromuscular training – has been
described for a range of sports and for young athletes at different stages of
maturation. The efficacy of each of these different components of physical
preparation for athletes in general, and young team sports players in
particular, is becoming increasingly well established. The nature of responses
to each of these forms of training at different stages of growth and maturation
has also been elucidated, albeit further research is necessary to provide a
clearer picture.
Any training programme should be geared to the physical and emotional
maturity of the individuals in the group. Due to the paucity of well-controlled
studies in the literature, there is a shortage of conclusive recommendations
regarding training design for young populations at different stages of
maturation (Naughton et al. 2000). That said, guidelines have been published
that differentiate between chronological age and, more importantly, biological
age (Bompa 2000; Faigenbaum et al. 2009; Kraemer and Fleck 2005).
Fundamentally, the primary emphasis of training for young team sports
players is on balanced physical development and building a foundation of
athleticism. Only once this is undertaken and physical maturation has taken
place should the focus then progressively shift to specialised preparation for
the particular sport and playing position.
Training recommendations for young players
As discussed, rates of growth and maturation within a group of young
athletes can vary widely. When training young team sports players it is
therefore difficult to define phases of development within a squad of players.
For the purposes of this section, guidelines will be divided into: ‘prepubescent’
– the stage of development prior to exhibiting physical signs indicating the
onset of puberty; ‘early puberty’ – defined as the phase between the onset of
puberty and attaining peak height velocity; and ‘adolescence’ – the period
following peak height velocity being attained and advancing into adulthood.
The divisions between stages are necessarily vague: the average age at
which peak height velocity is attained (marking the transition between ‘early
puberty’ and ‘adolescence’ as defined above) is around 12 years of age for girls
and 14 years for boys (Malina et al. 2004) but there is considerable variability
in this. Observing changes in physical characteristics, assessing
neuromuscular performance, and monitoring seated and standing heights at
regular intervals will help in determining the progression between stages. The
latter – standing and seated heights – are the most helpful objective measure
to track with young players when used to plot velocity curves (gain in height
per unit of time) for each player (Baxter-Jones and Sherar 2006). Seated height
is helpful as trunk length tends to lag behind leg growth. Ultimately it is
dependent on the coach to use their experience and observations of each
player’s performance during training over time as the deciding factor that
determines how and when to progress training for each individual player.
Within these guidelines, consideration must also be given to the training
age of the young player entering a programme of physical preparation. Prior
training experience – of strength training particularly – will influence
individual decisions regarding training prescription. For example, one player
who falls into the ‘early puberty’ category based on age and physical
characteristics who enters the programme with a background of two years
strength training may be ready for more complex training exercises more than
another player who is significantly older but has no prior strength training
experience. Regardless of the age or stage of growth and maturation of the
player, initial training prescription will reflect the primary objective of
developing competency performing fundamental movements and addressing
any functional deficits. Only once this has been undertaken should the focus
then shift to performance-related training goals and more advanced training.
Prepubescent players
Neuromuscular and movement skills training
Neuromuscular training should be initiated early in young players’ physical
preparation. This is important to help correct the valgus lower limb alignment
during athletic movements that is common in prepubescent athletes of both
genders (Barber-Westin et al. 2005). This form of training also has a role to
play improving the movement efficiency that has been identified as lacking
among these young players (Naughton et al. 2000).
The starting point for proven short-term neuromuscular training
programmes appropriate for young team sports players is instruction of
athletic position and safe movement mechanics (Hewett et al. 1999). This
fundamentals phase of established neuromuscular training protocols can be
implemented with young players during this stage of development. This
includes instruction and practice of jumping, landing and change of direction
movements as discrete skills. Neuromuscular movement skill training with
young athletes may be effectively augmented by postural balance and
dynamic stabilisation exercises (Myer et al. 2006). The emphasis with all
neuromuscular training exercises should be sound posture and correct lower
limb alignment for prepubescent players of both genders.
Metabolic conditioning
It follows that the lower capacity of prepubescents for anaerobic exercise
should be reflected in the training employed with these players. The majority
of training at this stage of development should be aerobic in nature. However,
the training modes used to achieve this may be skill-based to reduce training
monotony and include elements of fun and competition.
Skill- or game-related movement drills can be adapted for use as
conditioning activities. For example, an obstacle course can be constructed
involving different movements and ball skills, perhaps running relays between
teams of athletes (Bompa 2000). Alternatively, ball games with simplified rules
may be used – the numbers on each team and playing area can be
manipulated to alter exercise intensity. This less structured approach allows
the young player to self-regulate work intensity according to their individual
tolerance.
Strength training
In general, if a child is ready for participation in organised sports, they are
likely ready to undergo instruction and resistance training. However, for
young players with known or suspected medical conditions, medical clearance
should be sought prior to participation in resistance training, as with other
sports (Faigenbaum et al. 2009). The specific design of training for young team
sports players should be reflective of their stage of psychological and
emotional development, in order to engender motivation and facilitate
compliance (Stratton et al. 2004).
When coaching prepubescent players, it is important that training should be
enjoyable and give the young player an immediate sense of fun and
discovery-based learning (Stratton et al. 2004). In practical terms, the choice of
training exercises and loads used should be conducive to allow this approach
to be safely implemented. For example, body-weight resistance exercises are
more appropriate when training more complex whole-body movements.
A meta-analysis of training studies featuring children and adolescents of
varying ages has identified repetition schemes from 6–15 repetitions and 50–
100 per cent of 1–RM to be effective for resistance training with young
athletes (Falk and Tenenbaum 1996). In general, resistance training volumes of
two to three sets and frequency of training of two to three days per week
appear to be most effective. When young players are introduced to strength
training, light loads and high repetition schemes (12–15 repetitions) are most
appropriate (Faigenbaum et al. 2009). During this early stage of training
progression should be achieved by increasing number of sets performed and
number of exercises in the workout. The relative loading and number of
training days employed can then be increased at a later stage.
Figure 12.1 Swiss ball suspended row
Table 12.1 Training guidelines: prepubescent players
Adequate rest and recovery are key components of successful youth
resistance training. Younger players and those in the early stages of their
physical preparation will require more recovery time between training days.
Training on non-consecutive days is therefore recommended for prepubescent
players, in order to maximise the effectiveness of training and reduce the risk
of injury (Faigenbaum and Schram 2004).
Given that many of the benefits of strength training prior to puberty stem
from improved co-ordination, balance and proprioception, it follows that
exercise modes that favour development of these aspects should be
emphasised when training prepubescent players. Body weight resistance
exercises and free weights offer advantages from this point of view, in
comparison to fixed resistance machines, although these exercises may require
closer supervision. Another consideration if choosing to use resistance
machines with young players is that the apparatus must be fitted to the
dimensions of the young person. Some apparatus cannot be adjusted
sufficiently to be suitable for use (Faigenbaum et al. 2009).
Exercise selection should feature a combination of unilateral and bilateral
exercises appropriate to the young player’s capabilities. The inclusion of
unilateral exercises in prepubescent players’ training is important in order to
promote balanced development between limbs (Kraemer and Fleck 2005).
These exercises do not allow the young player to compensate with their
stronger limb as can happen with bilateral exercises. Bilateral exercises should
also feature in the young player’s programme at this stage of maturation as a
means to develop strength from a more stable base of support.
Early puberty
Neuromuscular and movement skills training
Puberty is characterised in males particularly by a progressive improvement
in neuromuscular abilities – this is known as the neuromuscular spurt
(Quatman et al. 2006). However, prior to attainment of peak height velocity
there may be short-term decrements in some aspects of neuromuscular
performance. It follows that neuromuscular training should be progressed
during this phase of the young player’s development in a way that is
responsive to his or her individual rate of neuromuscular development and
sensitive to any short-term changes.
Training to reduce the potentially injurious loading that occurs with poor
neuromuscular control of lower limb alignment assumes increased importance
given the gains in body mass that occur during puberty (which in turn
increases the loading and stresses imposed on joints and connective tissues).
In female players, this form of training is advocated as a means to artificially
create a ‘neuromuscular spurt’ similar to that which occurs naturally in males
during this phase of maturation (Quatman et al. 2006). Neuromuscular
training is a priority for female players to tackle the higher rates of lower limb
injury (in comparison to males) that become apparent from this stage of
maturation onwards (Lephart et al. 2005).
Neuromuscular training during this stage will continue to feature dynamic
balance and stabilisation work. These exercises have numerous progressions,
which can be implemented as appropriate with advances in maturation and
neuromuscular performance.
Metabolic conditioning
During and following puberty, metabolic training responses become
increasingly specific to the type of metabolic training employed. It follows
that the training modes used must account for this and increasingly reflect the
demands of the sport and playing position from this stage of maturation
onwards. Cross training activities will tend to feature less during the playing
season (however, these remain an important training tool particularly for
offseason training).
Depending on individual tolerance, intensity of metabolic conditioning will
likewise be progressively increased during this stage – in order to reflect the
higher intensities of exertion experienced during competitive games.
Conditioning games can be manipulated (reducing number of players each
side, modifying size of playing area, and so on) to become more demanding.
The rest intervals used between conditioning drills may also be decreased –
again within individual tolerance.
Figure 12.2 In-line single-leg squat
Strength training
Adequate rest and recovery continue to be an integral aspect when scheduling
strength training during puberty. Given the concomitant strains of growth
and maturation during this stage, recovery time is crucial between training
days. Strength training on nonconsecutive days therefore continues to be
advocated during puberty (Faigenbaum and Schram 2004).
Exercise selection will also reflect the need for balanced development and
improving strength for fundamental movements. General strength exercises
and unilateral exercises should feature prominently during puberty. With
advances in training experience, structural multi-joint lifts (variations of the
squat and deadlift) can be introduced. In the case of experienced young lifters,
Olympic-style lifts can also be integrated into the strength-training
programme as appropriate; under qualified supervision this form of training
carries no greater risk for young players than other athletic activities (Hamill
1994). Olympic lifts and their variations should be taught initially using a light
implement such as a broom handle or empty barbell, with the emphasis on the
quality of the lifting movement.
Whatever the exercise, the focus throughout should be on proper lifting
form, with loading limited until the young player has mastered lifting
technique. The coach should also be vigilant for temporary reductions in coordination and performance that may occur as the young player approaches
peak height velocity, and be prepared to modify exercise selection and loading
accordingly. Likewise, loading should be restricted from the point of view of
attenuating the stresses on skeletal and connective tissue structures during
phases of rapid growth (Naughton et al. 2000). Loading of the lumbar spine
particularly should be carefully monitored in recognition of the higher risk of
lumbar spine injury at this phase of development (Kujala et al. 1996).
Figure 12.3 Dumbbell split squat
Table 12.2 Training guidelines: early puberty
In the absence of corrective training, significant asymmetries are observed
both before and following puberty (Barber-Westin et al. 2006). From both
function and injury-prevention perspectives it is vital that any differences in
performance between dominant and non-dominant limbs are addressed
during this stage via strength training. Practical recommendations include
manipulating the number of repetitions and sets performed with each limb for
single-limb strength exercises (Cook 2003b). For example, the young player
may perform three repetitions on their weaker side for every two on their
dominant side (keeping the load constant).
For female players targeted hamstring strength training should begin
during this stage – ideally in conjunction with neuromuscular training to help
increase hamstring recruitment during dynamic activity (Hewett et al. 1999).
This is important to offset the quadriceps dominance that can increase strain
on the ACL in female athletes (Ford et al. 2003).
Adolescent players
Neuromuscular and movement skills training
The fundamental movement skills phase characteristic of earlier
neuromuscular training will be progressed during this stage of development to
more demanding jumping exercises and more sport-specific change of
direction drills. For all exercises the emphasis should remain on posture,
sound movement mechanics and correct lower limb alignment, particularly
during landing and change of direction movements (Myer et al. 2006).
As the player matures and their neuromuscular performance develops,
further advances in training may include single-leg plyometric-type jumping
and landing exercises in various directions, and unanticipated change of
direction movement drills. Postural balance and dynamic stabilisation
exercises can similarly be progressed during this stage by incorporating
various training devices to increase demand for balance and proprioception
(Myer et al. 2006a; Yaggie and Campbell 2006).
Metabolic conditioning
Aerobic endurance remains a training priority for adolescent players. A
continuing emphasis on appropriate metabolic conditioning would appear to
be vital for female players particularly, in order to counter the decline in
aerobic endurance that is otherwise observed in females after the onset of
puberty (Naughton et al. 2000).
In many team sports, adolescent players will require repeated sprint
conditioning to elicit appropriate anaerobic training effects (Naughton et al.
2000). Various modes of high-intensity interval conditioning can be effective –
including hill running (Helgerud et al. 2001) and high-intensity sport skill
conditioning drills (Hoff 2005; Hoff et al. 2002). By manipulating numbers on
each team, playing rules and playing area, skill-based conditioning games can
also elicit sufficiently high exercise intensities for repeated sprint conditioning
(Gamble 2004b; Hoff et al. 2002; Little and Williams 2006b).
Where it is appropriate to the sport, speed-endurance work may be
introduced into speed and agility work undertaken by players – providing that
the adolescent player is technically proficient. Prior to this stage in
development, any speed and agility training undertaken by players would
exclusively be categorised as neuromuscular training, with emphasis on
movement mechanics and complete recovery between repetitions.
As this is a stage of increasing specialisation in training, the training modes
used for individual training should be increasingly mode-specific. Given this,
by the time the young athlete reaches late adolescence it is probable that cross
training modes will only be emphasised during the off-season. By selecting
appropriate work bouts and rest–recovery intervals it is possible for highintensity interval training to elicit significant aerobic and anaerobic endurance
gains (Tabata et al. 1997). Over time it follows that the maturing player’s
aerobic endurance development may be predominantly achieved via high
intensity training (Little and Williams 2006b), particularly during the playing
season. However, these repetition schemes will, by definition, be highly
demanding and as such should be progressively introduced during late
adolescence. Skill-based conditioning games aimed at aerobic endurance
development employed in squad training should likewise become more
specific to the sport.
Strength training
Adolescent athletes are more conducive to a more adult longer-term approach
with regard to physical preparation undertaken in a more structured training
setting (Stratton et al. 2004). The starting point for any strength training will
depend on the adolescent player’s training history. If appropriate strength
development has occurred prior to and/or during puberty, then strength
training may be progressed to include a more advanced and sport-specific
exercise selection. However, if significant deficits are noted, the starting point
will be developing strength for fundamental movements and addressing
imbalances. In this case, initial exercise selection will be more reflective of
generic strength training for improved athleticism.
Assuming physical preparation has been undertaken prior to this stage of
maturation, training design should be increasingly based upon a
comprehensive needs analysis of the sport and playing position. As with
adults, exercise specificity influences young players’ responses to strength
training. Exercise selection should therefore be progressively sport-specific,
within the constraints of the skill level and training experience of the young
player.
Sport-specific exercise selection will vary according to the sport and
playing position. Typically, multi-joint lifts for speed-strength development
(Olympic-style lifts, barbell jump squats, and so on) that incorporate triple
extension of hips, knees and ankles will feature in the adolescent player’s
programme – given this is the principle biomechanical action common to
many dynamic movements in team sports (Gamble 2004a). Likewise,
unilateral support exercises should necessarily comprise a significant portion
of the young team sport athlete’s training – on the basis that the majority of
game-related movements are executed supported partly or fully on one or
other leg (McCurdy and Conner 2003). The reader is referred to Chapters 3
and 5 for guidelines on strength training and speed-strength training exercise
prescription.
Exercise selection from an injury prevention viewpoint should be based
upon injury data for the sport, and for the playing position where available.
Specifically, targeted strength-training exercises should be included in
adolescent players’ training to address areas identified as being prone to
injury in the sport (and playing position) – see Chapter 9 for this topic. In the
case of contact sports, hypertrophy may be an important programme goal for
adolescent players, to varying degrees depending on their playing position.
The shoulders should be an area for specific strengthening and hypertrophy,
as this is the site for impact forces during collisions with other players
(Gamble 2004a).
Table 12.3 Training guidelines: adolescent players
APPENDIX: PRACTICAL EXAMPLES OF TRAINING
DESIGN
Designing the programme: needs analysis
The basis for any training programme in any sport is a thorough needs
analysis. This process comprises two parts. The first task of a needs analysis is
objectively to define the demands and requirements of the sport and playing
position. The second aspect concerns the specific requirements of the player,
which will depend on the relative strengths of the individual as well as their
training and injury history.
Needs analysis for the sport comprises the biomechanics, bioenergetics and
injury profile of the sport and playing position. The biomechanics of a given
team sport can be qualitatively assessed by observing the predominant
movements and forms of locomotion involved during competitive play.
Bioenergetics refers to the relative contribution from different energy systems
during games. Time–motion and physiological data can be used to offer
insight into bioenergetics of the sport and playing position, if available
(Chapter 4). In the absence of relevant data from matches, elite players’
physiological test profiles can offer an insight into the relative contribution
and importance of different aspects (Chapter 2). Injury data for the sport and
playing position will similarly indicate the types of injuries players may be
exposed to during competition (Chapter 9), which will help to guide training
prescription (Chapter 10).
Needs analysis pertaining to the individual predominantly concerns their
training history, current assessment of strengths and weaknesses, and the
player’s injury history. Training history will influence exercise selection,
training progression and choice of periodisation scheme (Chapter 11).
Relevant test data for the player can be used to identify their strengths and
areas that require attention (Chapter 2), which will influence training design
in terms of the areas that require particular emphasis. The player’s injury
history will determine the areas that require ongoing rehabilitation and will
similarly guide exercise selection to help prevent re-injury (Chapter 10).
Example 1: Female team sport – women’s basketball
Off-season/early pre-season training cycle
Late pre-season training cycle
In-season training cycle
Peaking (in-season) training cycle
Example 2: Contact sport – rugby union football
Off-season training cycle
Early-mid pre-season training cycle
Early in-season training cycle
Peaking (in-season) training cycle
Example 3: Striking and/or throwing team sport–baseball
Early pre-season training cycle
Mid-late pre-season training cycle
Early in-season training cycle
Mid-season training cycle
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INDEX
ACL-agonist 171, 187, 231
acceleration 6, 18, 20–2, 32, 33, 55, 64, 83, 84, 92, 96, 100, 101, 104–6, 110, 112, 115, 119–24,
126–9, 132, 133, 135, 175, 207, 216, 218, 219
initial acceleration, first-step quickness 33, 119, 121, 122, 124, 125, 128
acceleration–deceleration profile 6, 13, 106
adenosine triphosphate see ATP
aerobic
capacity 23, 24, 59, 60, 63–6, 70, 71, 233, 234
endurance, fitness 23–5, 27, 53, 59, 70, 76, 225, 242
enzyme, oxidative enzyme 4, 62
exercise, conditioning, training 4, 191, 208, 223, 225, 233, 234, 236
interval training 62–6, 72, 215, 216, 218
metabolism, oxidative metabolism 4, 5, 59, 60, 62, 66, 67, 225
maximal aerobic speed ‘mas’, vVO2max 11, 23, 26, 63, 66
muscle oxidative capacity 4, 8, 60, 62, 63
power, maximal oxygen uptake, VO2max, VO2peak 23, 25, 65
agility
assessment, testing 32, 33, 120
development, training 119, 120, 122, 129, 132–5, 184, 207, 213, 215, 216, 218, 219, 242
performance 33, 119, 120, 123, 124, 129, 131, 133–5, 230
reactive 35, 36, 207, 216, 218, 219
American football 11, 17, 20, 34, 36, 57, 68, 74, 80, 81, 95, 102, 105, 133, 161, 167, 168, 172,
178, 217, 224
agonist
muscle, motor units 98, 99, 103, 105, 110, 111, 113, 114, 116
anaerobic
capacity 5, 23, 29, 30, 58, 62, 65, 235, 243
endurance, fitness 53, 76, 242
enzyme 4, 61, 66, 225
exercise, conditioning, training 4, 225, 233–6, 242
interval training 65, 66, 191, 216, 218, 243
metabolism, energy system 4, 5, 25, 26, 55, 56, 59, 66, 225, 234
power see power, anaerobic power, explosive power
threshold see lactate threshold
antagonist muscle, antagonist motor units 99, 103, 105, 106, 113, 114, 116
antagonist co-contraction 103, 105, 10
arm action, arm drive, arm swing 20, 21, 121, 127, 133
athleticism 22, 51, 75, 214, 221, 222, 230, 235, 242
ATP (adenosine triphosphate) 58, 62
Australian Rules football 20, 25, 36, 125, 129, 165, 172–5
balance 15, 19, 21, 22, 36–8, 45, 46, 49, 77, 84, 92, 123, 128, 197, 223, 238
assessment, testing 36, 37, 41, 42, 45–8
board, device, disk, wobble board, domed device 36, 39, 41, 42, 48–50, 145, 146, 147, 148,
185, 192, 195, 242, 243
dynamic postural 37, 45, 47–9, 128, 132, 137, 184, 185, 189, 207, 231, 239
dynamic stabilisation 37, 45, 48, 167, 184, 185, 188–90, 207, 236, 239, 242, 243
exercise, training, sensorimotor training 42, 47–9, 146, 185–7, 197, 207, 231, 236, 239
postural, static, postural stability 22, 36–9, 45–8, 128, 167, 185, 188–90, 207, 231, 236, 241,
243
ballistic
action, exercise, movement 18, 96, 97, 106, 112, 114, 115, 117, 125, 179
training, resistance training 7, 17, 100, 101, 104–8, 112–15, 118, 125, 207, 216, 218, 219
baseball 77, 99, 106, 116, 140, 155, 156, 179, 200, 210
basketball 10, 12, 22, 49, 54, 59, 69, 77, 102, 115, 121, 122, 154, 155, 159–61, 167, 168, 170, 185,
210
bilateral 5, 21, 22, 37, 77, 83, 85, 87, 103, 108, 112, 125, 129, 131, 174, 216, 238, 239
change of direction
activity, movement 34, 35, 47, 49, 52, 55, 61, 64, 67, 96, 119, 120, 123, 129, 131–5, 141–3,
146, 151, 168, 170, 173, 175, 236, 241
performance, speed 21, 32–5, 49, 103, 119, 120, 123, 129, 131, 134
tests, assessment, measures 21, 32–6, 120, 132
training 132, 133, 207, 215, 216, 218, 219, 241
concentric
movement, contraction, action 5, 6, 14–16, 20–2, 86, 97, 98, 100, 102, 103, 105, 106, 108–11,
123, 148, 173, 190, 193
performance, force development 20, 22, 40, 102, 106, 111, 118
power, rate of force development, speedstrength 17, 20, 22, 39, 95, 98, 103, 104, 106, 109,
111, 118, 125, 141, 172, 193, 199
strength 15, 16, 129, 131, 159, 174, 179, 191, 199
co-ordination
intermuscular 42, 61, 76, 82, 84, 92, 98, 99, 103, 106, 107, 114, 116, 127, 128, 135, 177, 229
intramuscular 61, 74, 82, 84, 92, 94, 97, 98, 103, 106, 110, 114, 128, 229
neuromuscular 19, 20, 21, 42, 44, 61, 64, 76, 83, 85, 87, 88, 98, 102, 118, 119, 127–9, 133, 140,
177, 196, 212, 218, 222, 229, 230, 231, 238, 240
training 114–18, 126, 128, 207, 218
core
endurance 137, 141, 143, 144, 177
lumbopelvic control, posture 49, 131, 132, 142, 143, 150, 171, 173, 174, 187, 191
lumbopelvic region, trunk, muscles, musculature 38, 39, 83, 88, 89, 99, 121, 132, 136–44,
146, 148, 152
lumbopelvic stability 38, 39, 83, 126, 131, 136–8, 140–5, 148, 150, 152, 172, 174, 176, 188,
190, 191, 195, 197, 225
strength 143, 144, 146, 147, 152, 171, 188
training, exercises 136, 141, 143–8, 150, 152, 187, 188, 190, 196
countermovement 6, 20, 97, 106, 111, 112
horizontal jump: see jump, horizontal
vertical jump: see jump, vertical
cricket 99
cross training 3, 4, 64, 206, 215, 228, 234, 239, 242
deceleration 55, 105, 119, 120, 123, 132, 135, 141, 170
decision-making 7, 33, 70, 119, 120, 123, 124, 129, 133–5
drop jump see jump, drop jump
dynamic
correspondence 78, 82, 84, 85, 87, 88, 94
stabilisation: see balance, dynamic stabilisation
eccentric
action, contraction, movement, phase 6, 14–16, 20, 22, 40, 86, 98, 106, 109, 110, 111, 118,
123, 148, 156, 173, 179, 187, 189, 190
exercise, training 5, 6, 148, 182, 189, 190, 193
loading 112, 141, 173, 175, 190,
strength 15, 16, 111, 112, 129, 159, 172, 174, 179, 187, 191, 193, 194, 199
economy
running, work 23, 28, 60, 61, 64–7, 76, 224
elastic
elements 76, 113
energy, storage, return 98, 110, 111, 121
series 76, 113
elasticity, tendon compliance 76, 98
electronic timing 32–4
endurance
assessment, measures, tests 23–5, 27, 30, 38, 74, 76, 137, 142, 152, 235
athletes 24, 65, 76, 114
exercise, training 3, 5, 11, 61, 212, 233, 234
performance 2, 23–5, 27, 28, 53, 58, 63–5, 71, 76, 213
extensor muscle, muscles 111, 121, 138, 142, 152, 177
extensors
hip 5, 38, 177, 191
knee 77, 126, 127, 159, 172
extrinsic risk, risk factors see injury, injury risk
fatigue 3, 25, 30, 31, 42, 58, 61, 70, 74–6, 92, 93, 113, 138, 153, 155, 156, 158, 173, 174, 176, 178,
181, 191, 195, 197, 198, 205, 206, 209–11, 213, 218, 219, 222, 239
fatigue index 31
field-based assessment, testing 12–14, 20, 21, 23–33, 35–40, 46, 47, 66
field sports 33, 36, 67, 81, 122, 168, 175
fitness–fatigue model 3, 204
flexibility 39, 40, 83, 154, 156, 172, 173, 176, 190, 191, 195, 203, 230, 231
training, exercises 191, 192, 195, 197, 200, 203, 230
flexor muscle, muscles 38, 152, 177
flexors
hip 146, 173, 191, 192
knee flexors 40, 193
flight phase, swing phase 45, 109, 122, 128, 151, 173, 193
foot 39, 46, 48, 77, 121, 123, 127, 128, 132, 133, 142, 160, 161, 168, 170, 171, 175
contact, foot strike 76, 110–12, 119–22, 125, 126, 128, 131, 232
forefoot 121
heel, rearfoot 39, 121, 126, 155, 226
midfoot 121, 126
football
soccer see soccer, association football
American see American football
Australian Rules see Australian Rules football
rugby see rugby football
force 5–8, 14–16, 18, 19, 22, 37, 43, 46, 49, 61, 76, 78, 81, 83, 84, 87, 94–103, 105, 106, 108, 111–
13, 115, 118, 121, 124, 125, 127, 131–3, 135, 137–41, 143–5, 156, 157, 167, 168, 170, 171, 173,
176, 178, 179, 187, 189, 191, 196, 199, 203, 223, 225, 229–32, 243
braking 121, 123, 126
ground reaction 16, 21, 37, 87, 111, 120, 121, 123, 128, 129, 132, 133, 225, 232
propulsion 101, 102, 110, 121, 128, 131
force-velocity curve, relationship 6, 14, 94–7, 108
force-time curve 18, 96, 116, 126
frequency
injury see injury rate, frequency
training 4, 42, 44, 56, 65, 69, 78–80, 83, 84, 106, 182, 183, 186, 206, 214–19, 237, 239, 243
glycogen, muscle glycogen 60–2
glycolysis, glycolytic metabolism, system 56, 58, 59, 61, 225, 233, 234
glycolytic enzyme 58, 61
ground contact time 22, 97, 110, 112, 125, 126
ground reaction force see force, ground reaction force
handball 22, 69, 70, 200
heart rate 11, 23, 27, 28, 55, 61, 71
high-intensity
activity, effort 8, 25, 26, 30, 53, 54, 56–60, 66
interval training, conditioning 4, 5, 60, 62–8, 70–2, 191, 233, 235, 242
training, conditioning 63–5, 112, 174, 187, 210, 218, 219, 234, 242
hip girdle, hip complex 19–21, 38, 39, 46, 86, 88, 116, 120–3, 125–8, 129, 133, 136–8, 140–3,
145–8, 150, 151, 154, 156, 171, 172, 174–7, 187, 188, 190, 191, 195–7, 203, 243
hockey
field 24, 121, 133
ice 21, 25, 26, 57, 77, 121, 133, 155, 165, 166, 168, 175, 176, 178, 195, 210
hydrogen ions, H+ 58, 59, 63, 234
injury 5, 37, 39, 40, 44, 47, 49, 76, 77, 85, 134, 138, 141–3, 146, 153–8, 160–79, 181–91, 193–200,
203, 213, 222, 223, 225, 226, 228–32, 243
frequency 36, 41, 44, 49, 51, 70, 75, 83, 137, 141, 153–5, 157–65, 167–70, 173, 174, 178–82,
185, 187, 190, 191, 193, 194, 196–8, 222, 225, 231, 239
history 40, 85, 141, 152, 154, 165–9, 174–6, 178, 182, 184–6, 193, 195–7
mechanism 76, 142, 146, 153–5, 158, 160, 161, 165, 167–9, 171–6, 179–82, 187, 188, 190, 191,
203
prevention 40, 41, 44, 76, 83, 134, 136, 153, 154, 166, 167, 181–4, 187, 191, 193, 196, 197,
199, 200, 203, 211, 222, 230–2, 241, 243
rate 36, 41, 44, 49, 51, 70, 75, 83, 137, 141, 153–5, 157–65, 167–70, 173, 174, 178–82, 185,
187, 190, 191, 193, 194, 196–8, 222, 225, 231, 239
risk 37–41, 75, 105, 117, 142, 146, 153–5, 163, 164, 169–71, 173, 175, 176, 178, 181, 183, 185–
7, 191, 192, 195, 197, 221–3, 230, 238, 240
severity 153, 158, 163, 164, 166, 174, 178, 180, 198, 230, 231
injury risk factor 51, 141, 153, 158, 163, 166, 167, 173, 174, 176, 181, 185, 188, 195, 203, 231
extrinsic risk, risk factor 153, 154, 155, 165, 179, 180
intrinsic risk, risk factor 39, 153, 154, 165, 179–81, 183
intensity
training, work 4, 5, 11, 12, 23, 25, 26, 28–30, 42, 53, 55, 56, 61–3, 65, 66–73, 78–80, 83, 92,
111, 118, 143–5, 152, 182–4, 206, 208–10, 212–19, 233, 234, 237, 239, 241, 243
intermittent
activity, exercise 23, 25, 26, 54–8, 65, 68, 71
sports 23–5, 54
intervals
rest intervals see recovery, rest
work 5, 25, 26, 66, 68
jump, jumping 6, 9, 19–22, 38, 46, 49, 86, 96, 101–3, 109, 111, 121, 170, 172, 186, 190, 221, 230,
232, 236, 241
drop, depth 22, 44, 46, 47, 49, 51, 109–12, 131, 189
horizontal 21, 22, 110, 114, 230
squat 6, 13, 18, 19, 105–8, 113, 114, 118, 125, 126, 145, 243
vertical 6, 10, 20–3, 41, 49, 51, 78, 83, 94, 95, 101–3, 105, 108–12, 114, 121, 125, 127, 129, 230
kinematic, kinematics 6, 21, 44, 52, 53, 81, 82, 92, 94, 101, 110, 123–8, 133, 140, 143, 156, 170
kinetic chain
lower limb 5, 15, 17, 46, 77, 86, 99, 115, 128, 132, 142, 143, 195, 203
kinetics 6, 44, 51, 73, 82, 94, 101, 123, 127, 143, 156
lacrosse 133, 168, 170
lactate 23, 26, 28, 29, 55–9, 62, 63, 234
handling 23, 28, 29, 58, 59, 62, 63, 81, 234
maximum steady state (MLSS) 23, 28, 29, 62, 63, 65, 235
threshold 23, 28, 29, 62, 63, 65, 235
lumbar
spine, vertebrae 38, 136–8, 140, 142, 145, 146, 152, 164, 175–7, 196, 197, 222, 226, 240
lumbo-pelvic-hip complex 136–8, 142, 171, 187, 197
lumbopelvic
posture 141, 144, 151, 173, 174, 191, 197
stability see core stability
macrocycle, training macrocycle 8, 84, 92, 104, 118, 206–8
maturation 43, 44, 170, 221, 223–7, 229, 234–6, 238–40, 243
mesocycle, training mesocycle 204, 208, 209, 210, 213, 215, 216, 218, 219, 220
metabolic conditioning 4, 8, 53, 61, 64, 65, 67–72, 76, 92, 153, 181, 191, 206, 211–13, 215, 216,
218, 219, 221, 225, 233–6, 239, 241–3
metabolic pathways, processes 1, 3, 5, 7, 8, 30, 53, 55, 57, 58, 71, 83, 225
microcycle, training microcycle 208–10, 212, 216–18
mobility 40, 42, 77, 80, 92, 154, 159, 177, 197, 203, 228
morphological adaptations 78, 84, 99, 116, 117, 221
morphology 8, 105
motor
control 7, 70, 84, 93, 136, 144, 145, 185, 231
cortex, higher motor centres 98, 106, 110, 113
learning, development 7, 21, 42, 134, 222
patterns, strategies 8, 10, 13, 22, 27, 40, 42, 49, 61, 71, 105, 114–16, 127, 141, 145, 177, 186,
196
performance, skills 7, 8, 12, 20, 43, 95, 99, 114, 116, 133, 214, 222, 224, 227, 229, 230
unit 63, 74, 78, 96–8, 102, 103, 106, 113, 116, 128, 184
movement
athletic 15, 42, 43, 47, 49, 51, 73, 77, 81, 92, 94, 96–9, 104, 105, 117, 132, 143, 144, 171, 187,
190, 214, 226, 228, 236, 239, 240, 242
athleticism, competency, dexterity 49, 51, 236
fundamental 15, 42, 43, 47, 49, 51, 73, 77, 81, 92, 94, 96–9, 104, 105, 117, 132, 143, 144, 171,
187, 190, 214, 226, 228, 236, 239, 240, 242
fundamental abilities 15, 40, 42, 43, 77, 81, 228
mechanics 20, 22, 32, 40, 49, 120, 123, 127, 129, 133, 155, 186, 187, 221, 222, 225, 236, 241,
242
response, strategy 7, 35, 36, 70, 124, 127, 134, 197
screening, profiling, movement screens 39, 40, 41, 46, 73, 154, 214
skill development, training 43, 49, 51, 133, 186, 187, 196, 197, 207, 216, 221, 222, 228, 236,
238, 239, 241, 243
task 5–8, 10, 12–23, 27, 32, 35–8, 40, 42, 44–9, 51, 52, 54, 55, 64, 65, 67, 70, 72, 74, 77, 81–4,
86–9, 92–4, 96–104, 106–10, 112–19, 121, 123–5, 127–9, 131–4, 136, 137, 139–41, 143,
144, 146, 148, 150, 151, 155, 156, 170–2, 176, 179, 181, 184, 187, 189, 190, 193, 196–200,
214, 224, 226, 229, 231, 232, 234, 236, 237, 243
velocity 8, 10, 13–15, 55, 64, 96, 97, 99, 115, 116, 119, 128, 223
muscle, muscle group 1, 3–7, 21, 26, 38–40, 46, 59, 61, 63, 67, 75–7, 79, 80, 82–5, 88, 89, 94, 98–
100, 103, 105, 106, 110, 111, 113, 114, 116, 122–5, 127, 129, 136–48, 150, 152–7, 159, 171–9,
181–7, 189–91, 193–200, 203, 209, 213, 222, 224–6, 229, 230, 232, 234
action, contraction 5, 8, 22, 106, 113, 156
buffering capacity 23, 58, 62
cell 58–60, 63, 97, 100, 105, 110, 225
fascicle 97, 103, 106, 110
fibre 58–60, 63, 97, 100, 105, 110, 225
function 10, 13, 46, 99, 141, 169, 171–4, 176–9, 191, 196–8
oxidative capacity 60, 62, 63
strain injury 39, 40, 154, 157–9, 162, 164–6, 173–6, 191, 192, 194, 195
muscle–tendon complex, musculotendinous unit 61, 76, 103, 106, 109–11, 113, 173
musculoskeletal
assessment, screening 39–41, 73, 154, 182, 214
system 39, 75, 98, 136, 155, 157, 159, 172, 181, 225, 229
needs analysis 8, 166, 243
netball 36, 99, 115, 116, 161
neuromuscular
adaptation 44, 61, 64, 103, 110, 117, 126, 182, 186
control 42, 43, 45–7, 49, 52, 61, 76, 84, 92, 123, 131, 133, 140–4, 171, 172, 181, 183, 185, 198,
203, 221, 223, 225, 230, 239
co-ordination, skill 37, 40, 42–4, 64, 65, 81, 87, 92–4, 98, 102, 119, 124, 128, 129, 132, 133,
135, 212, 218
function, performance 4, 7, 10, 13, 17, 23, 39, 40, 42, 43–6, 51, 52, 57, 58, 60, 61, 71, 72, 76,
82, 83, 95, 167, 177, 183, 184, 187, 190, 196, 221, 224, 225, 227, 235, 238, 239, 241–3
‘spurt’ 43, 224, 225, 238, 239
system 2, 3, 78, 82, 94, 95, 97, 100, 140
training 42–5, 47, 49, 51, 52, 64, 93, 127, 132, 134, 144, 153, 166, 182, 184, 186–8, 196, 197,
207, 211, 221, 223, 225, 228, 235, 236, 238, 239, 241
Olympic lifts 19, 92, 93, 95, 100–4, 106, 118, 125, 207, 208, 216, 218, 229, 240, 241, 243
Olympic-style weightlifting 19, 92, 93, 95, 100–4, 106, 118, 125, 207, 208, 216, 218, 229, 240,
241, 243
oxidative
capacity see muscle oxidative capacity
enzyme see aerobic enzyme
metabolism see aerobic metabolism
peak height velocity 221, 224, 225, 235, 239, 240
pelvis, pelvic girdle 38, 46, 99, 126, 132, 136–8, 140, 141, 145, 146, 151, 173, 174, 176, 177, 191,
192, 196, 197
perception, perceptual aspects 6, 36, 119, 120, 123, 129, 134, 135
perception-action coupling 7, 119, 124, 128, 129, 133
periodisation, periodised training 72, 102, 118, 152, 182, 204–20
phosphocreatine, PCr 60, 62, 67
plantarflexor see extensors, ankle extensors
plyometric
action, activity, exercise 92, 109–12, 125, 131, 213, 232, 241
training 9, 17, 22, 98, 106, 108–12, 118, 125, 126, 131, 135, 187, 207, 215, 216, 218, 219, 231,
232
plyometrics
fast SSC 22, 98, 109, 110, 112, 125, 126, 131, 135, 207, 218, 219
slow SSC 20, 22, 98, 103, 109, 110, 112, 125, 131, 135, 207, 216, 218
power
anaerobic, explosive, speed-strength 2, 7, 17–23, 26, 30, 31, 35, 39, 59, 61, 73–6, 78, 81, 83,
85, 93–115, 117, 118, 121, 124, 125, 128, 129, 141, 145, 211–13, 217, 218, 219, 225, 230
development, training 11, 94, 95, 99–115, 117, 118, 121, 124, 128, 129, 204, 206, 208, 212,
215, 216, 219
range of motion, movement 5, 7, 8, 15–17, 39, 77, 82, 85, 100, 104, 105, 154, 156, 176, 189, 195,
197, 200, 230
rate of force development ‘RFD’ 6, 7, 8, 10, 17, 92, 96, 100, 101, 103, 105, 111, 112, 116
recovery, rest 5, 8, 26, 30, 31, 57, 59–62, 64, 66, 67, 92, 113, 118, 178, 197, 213, 220, 238–43
recovery
action, recovery phase (of sprinting action) 122, 128
active 26, 57, 209, 213, 218
rest 5, 8, 26, 30, 31, 57, 59–62, 64, 66, 67, 92, 113, 118, 178, 197, 213, 220, 238–43
reflex
local spinal reflexes 98, 187
‘stretch reflex’ 98, 111
repeated sprint
ability, performance 23, 30–2, 57–60, 63–65, 70, 71, 76
activity, repeated sprints 25, 30, 31, 57–62, 65, 174
conditioning, sprint interval training 4, 61–3, 67, 68, 71, 72, 216, 218, 219, 242
rugby
football 73, 74, 101, 102, 133, 170, 172, 174, 178, 214
league 19, 70, 101, 164, 210
union 54, 59, 79, 163, 164, 178, 211
running mechanics, stride mechanics 76, 120, 121, 122, 126–8, 133, 222
scheduling, schedule 14, 84, 197, 205, 208, 213, 214, 218–20, 226, 227, 240
shuttle run, shuttle running
assessment, testing, tests 23–6, 30, 31, 34, 58, 64, 68, 95, 235
performance 55, 58, 61, 64, 68, 70, 72
soccer, association football 22–6, 29, 30, 32, 34–7, 40, 44, 53, 54, 57, 60, 62, 65–7, 69, 71, 75,
115, 120, 122, 154, 157, 158, 166, 170–6, 181, 182, 185, 190, 191, 195, 211, 214, 218, 224, 227,
235
softball 23, 83, 200
speed
assessment, measures, testing 13, 17, 20–2, 26, 30–4, 41, 55, 74, 101, 110, 112, 120, 124–6,
224, 230
development, training 49, 61, 64, 72, 101, 117, 119, 120, 122, 124–9, 135, 185, 207, 212, 213,
215, 216, 218, 219, 242, 243
running speed 2, 13, 24–6, 28, 45, 55, 58, 60, 61, 64, 66, 68, 74, 77, 78, 103, 109, 110, 112,
119–29, 134, 135, 146, 173, 175, 211, 212
speed-endurance
conditioning, training 219, 242, 243
performance 74, 219
speed-strength
exercise, training modes 6, 18, 72, 76, 92, 94, 95, 99–102, 104, 105, 109, 111, 112, 113, 116–
18, 129, 134, 135, 207, 215, 216, 218, 219, 243
reactive 22, 111
see also power
split stance 103, 108, 125
spring-mass characteristics 61, 106
sprints, sprinting 4, 5, 8, 13, 19, 20, 22, 30, 31, 34–6, 57–61, 64, 65, 67, 68, 72, 78, 103, 108–12,
120–9, 131, 135, 146, 232
sprint training: see speed development, training
sprint interval training: see repeated sprint conditioning
stability
joint 37, 136, 137, 141, 144, 154, 155, 161, 167–70, 177, 178, 179, 184–6, 188, 189, 197, 198,
203, 225, 228, 230–2
torsional 39, 148, 157
stance phase 122, 128, 173, 193
stiffness
joint stiffness 170
lower limb 61, 98, 128
musculotendinous 61, 76, 109, 110, 113
spine, torso 61, 99, 121, 137, 139, 141, 143, 146, 152
strength
assessment, measures, testing 5, 10, 11, 14–17, 19, 20, 40, 43, 73, 75, 77, 78, 81, 93, 95–7,
101, 105, 114, 129, 154, 156, 159, 171, 176, 179, 187, 191, 195, 196, 199, 219, 231
concentric 15, 16, 174, 179, 191, 199
eccentric 15, 16, 159, 172, 174, 179, 187, 189, 191, 193, 194, 199
expression, performance 2, 9, 14, 15, 17, 21, 60, 73–6, 79, 80, 83, 84, 94, 96–100, 103, 112,
116, 117, 119, 125, 132, 137, 141, 144, 169, 173, 174, 177, 186, 193, 198, 199, 211, 213, 215,
217, 223, 224, 226
isometric strength 14, 15, 172, 176, 177
reactive strength 20, 22, 125, 129, 131, 135
training adaptation, response 5–7, 13, 43, 79–83, 95, 106, 117, 143, 152, 156, 171, 181, 194,
198, 199, 203, 211, 220, 226, 229, 230, 232, 238
training, development 3, 4, 5, 6, 8, 9, 11, 17, 42, 65, 72–89, 92–4, 96, 97, 99–102, 104–6, 112,
114, 117, 124, 125, 129, 131, 143, 146–8, 150, 152, 153, 155, 164, 166, 176, 181, 182, 184–
7, 189–91, 193–200, 204, 206–8, 211–19, 221, 224, 226, 228–33, 235–8, 240–3
strength-endurance 17, 73, 74, 76, 81, 83, 92, 195, 198, 199, 206, 215
stretch reflex see reflex, stretch reflex
stretch, pre–stretch 97, 98, 110, 111, 173, 174
stretching 191, 192, 199, 230
stretch-shortening cycle ‘SSC’ 20, 22, 76, 97, 98, 103, 109–12, 119, 125, 126
fast SSC: see plyometrics, fast SSC
slow SSC: see plyometrics, slow SSC
stride frequency, stride rate 121, 127
stride mechanics see running mechanics
swing phase see flight phase
team sports 3, 6, 8, 10–14, 16, 17, 20, 22–6, 28–37, 44, 51, 53–62, 64, 65, 67–9, 71, 73–7, 79–86,
92, 93, 95, 101, 102, 107, 115, 118, 119, 121–5, 129, 132, 135, 141, 142, 144, 145, 152–5, 163,
166–70, 172, 174, 175, 177, 179–82, 186, 193, 196, 200, 204, 210–15, 217, 221–4, 227, 228,
230, 234–7, 242, 243
tendon 98, 103, 106, 110, 159, 162, 164, 172, 182, 189, 190, 226, 232
toe-off 122, 127, 128
training volume 4, 12, 42, 61–63, 65, 72, 73, 78–81, 84, 92, 111, 113, 155, 172, 174, 182, 183, 204,
206, 208–16, 218, 219, 226, 228, 232, 234, 237, 239, 241, 243
transfer, transfer of training effects 1, 7, 8, 51, 65, 73, 75, 77, 78, 82–4, 92, 94, 95, 101–4, 108,
109, 114–16, 118–20, 125, 126, 135, 136, 205
transfer training 88, 133, 207, 218, 219
unilateral 5, 22, 23, 37, 83, 85, 86, 87, 92, 108, 110, 125, 126, 131, 135, 148, 189, 216, 218, 219,
238–41, 243
velocity 6, 15, 18, 19, 32, 33, 54, 55, 64, 95–7, 99–101, 105, 108, 110, 115–18, 122–9, 134, 144,
156, 184, 216
VO2max, maximal oxygen uptake: see aerobic power, maximal oxygen uptake
VO2peak, peak oxygen uptake: see aerobic power, maximal oxygen uptake
vVO2max, velocity at VO2max: see aerobic, maximal aerobic speed
volleyball 9, 21, 22, 36, 49, 69, 70, 102, 122, 159, 168, 172, 179, 186, 200
volume, training volume 4, 12, 42, 61–3, 65, 72, 73, 78–81, 84, 92, 111, 113, 155, 172, 174, 182,
183, 204, 206, 208–16, 218, 219, 226, 228, 232, 234, 237, 239, 241, 243
volume load 83, 84, 210
warm up 44, 115, 145, 152, 173, 183, 184, 190, 230, 241